Migrate from dep to go module

Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>

vendor/github.com/opencontainers/go-digest/.mailmap

@@ -0,0 +1 @@
+Stephen J Day <stephen.day@docker.com> <stevvooe@users.noreply.github.com>

vendor/github.com/opencontainers/go-digest/.pullapprove.yml

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+approve_by_comment: true
+approve_regex: '^(Approved|lgtm|LGTM|:shipit:|:star:|:\+1:|:ship:)'
+reject_regex: ^Rejected
+reset_on_push: true
+author_approval: ignored
+signed_off_by:
+  required: true
+reviewers:
+  teams:
+  - go-digest-maintainers
+  name: default
+  required: 2

vendor/github.com/opencontainers/go-digest/.travis.yml

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+language: go
+go:
+  - 1.7
+  - master

vendor/github.com/opencontainers/go-digest/CONTRIBUTING.md

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+# Contributing to Docker open source projects
+
+Want to hack on this project? Awesome! Here are instructions to get you started.
+
+This project is a part of the [Docker](https://www.docker.com) project, and follows
+the same rules and principles. If you're already familiar with the way
+Docker does things, you'll feel right at home.
+
+Otherwise, go read Docker's
+[contributions guidelines](https://github.com/docker/docker/blob/master/CONTRIBUTING.md),
+[issue triaging](https://github.com/docker/docker/blob/master/project/ISSUE-TRIAGE.md),
+[review process](https://github.com/docker/docker/blob/master/project/REVIEWING.md) and
+[branches and tags](https://github.com/docker/docker/blob/master/project/BRANCHES-AND-TAGS.md).
+
+For an in-depth description of our contribution process, visit the
+contributors guide: [Understand how to contribute](https://docs.docker.com/opensource/workflow/make-a-contribution/)
+
+### Sign your work
+
+The sign-off is a simple line at the end of the explanation for the patch. Your
+signature certifies that you wrote the patch or otherwise have the right to pass
+it on as an open-source patch. The rules are pretty simple: if you can certify
+the below (from [developercertificate.org](http://developercertificate.org/)):
+
+```
+Developer Certificate of Origin
+Version 1.1
+
+Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+1 Letterman Drive
+Suite D4700
+San Francisco, CA, 94129
+
+Everyone is permitted to copy and distribute verbatim copies of this
+license document, but changing it is not allowed.
+
+
+Developer's Certificate of Origin 1.1
+
+By making a contribution to this project, I certify that:
+
+(a) The contribution was created in whole or in part by me and I
+    have the right to submit it under the open source license
+    indicated in the file; or
+
+(b) The contribution is based upon previous work that, to the best
+    of my knowledge, is covered under an appropriate open source
+    license and I have the right under that license to submit that
+    work with modifications, whether created in whole or in part
+    by me, under the same open source license (unless I am
+    permitted to submit under a different license), as indicated
+    in the file; or
+
+(c) The contribution was provided directly to me by some other
+    person who certified (a), (b) or (c) and I have not modified
+    it.
+
+(d) I understand and agree that this project and the contribution
+    are public and that a record of the contribution (including all
+    personal information I submit with it, including my sign-off) is
+    maintained indefinitely and may be redistributed consistent with
+    this project or the open source license(s) involved.
+```
+
+Then you just add a line to every git commit message:
+
+    Signed-off-by: Joe Smith <joe.smith@email.com>
+
+Use your real name (sorry, no pseudonyms or anonymous contributions.)
+
+If you set your `user.name` and `user.email` git configs, you can sign your
+commit automatically with `git commit -s`.

vendor/github.com/opencontainers/go-digest/MAINTAINERS

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+Aaron Lehmann <aaron.lehmann@docker.com> (@aaronlehmann)
+Brandon Philips <brandon.philips@coreos.com> (@philips)
+Brendan Burns <bburns@microsoft.com> (@brendandburns)
+Derek McGowan <derek@mcgstyle.net> (@dmcgowan)
+Jason Bouzane <jbouzane@google.com> (@jbouzane)
+John Starks <jostarks@microsoft.com> (@jstarks)
+Jonathan Boulle <jon.boulle@coreos.com> (@jonboulle)
+Stephen Day <stephen.day@docker.com> (@stevvooe)
+Vincent Batts <vbatts@redhat.com> (@vbatts)

vendor/github.com/opencontainers/go-digest/README.md

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+# go-digest
+
+[![GoDoc](https://godoc.org/github.com/opencontainers/go-digest?status.svg)](https://godoc.org/github.com/opencontainers/go-digest) [![Go Report Card](https://goreportcard.com/badge/github.com/opencontainers/go-digest)](https://goreportcard.com/report/github.com/opencontainers/go-digest) [![Build Status](https://travis-ci.org/opencontainers/go-digest.svg?branch=master)](https://travis-ci.org/opencontainers/go-digest)
+
+Common digest package used across the container ecosystem.
+
+Please see the [godoc](https://godoc.org/github.com/opencontainers/go-digest) for more information.
+
+# What is a digest?
+
+A digest is just a hash.
+
+The most common use case for a digest is to create a content
+identifier for use in [Content Addressable Storage](https://en.wikipedia.org/wiki/Content-addressable_storage)
+systems:
+
+```go
+id := digest.FromBytes([]byte("my content"))
+```
+
+In the example above, the id can be used to uniquely identify 
+the byte slice "my content". This allows two disparate applications
+to agree on a verifiable identifier without having to trust one
+another.
+
+An identifying digest can be verified, as follows:
+
+```go
+if id != digest.FromBytes([]byte("my content")) {
+  return errors.New("the content has changed!")
+}
+```
+
+A `Verifier` type can be used to handle cases where an `io.Reader`
+makes more sense:
+
+```go
+rd := getContent()
+verifier := id.Verifier()
+io.Copy(verifier, rd)
+
+if !verifier.Verified() {
+  return errors.New("the content has changed!")
+}
+```
+
+Using [Merkle DAGs](https://en.wikipedia.org/wiki/Merkle_tree), this
+can power a rich, safe, content distribution system.
+
+# Usage
+
+While the [godoc](https://godoc.org/github.com/opencontainers/go-digest) is
+considered the best resource, a few important items need to be called 
+out when using this package.
+
+1. Make sure to import the hash implementations into your application
+    or the package will panic. You should have something like the 
+    following in the main (or other entrypoint) of your application:
+   
+    ```go
+    import (
+        _ "crypto/sha256"
+   	    _ "crypto/sha512"
+    )
+    ```
+    This may seem inconvenient but it allows you replace the hash 
+    implementations with others, such as https://github.com/stevvooe/resumable.
+ 
+2. Even though `digest.Digest` may be assemable as a string, _always_ 
+    verify your input with `digest.Parse` or use `Digest.Validate`
+    when accepting untrusted input. While there are measures to 
+    avoid common problems, this will ensure you have valid digests
+    in the rest of your application.
+
+# Stability
+
+The Go API, at this stage, is considered stable, unless otherwise noted.
+
+As always, before using a package export, read the [godoc](https://godoc.org/github.com/opencontainers/go-digest).
+
+# Contributing
+
+This package is considered fairly complete. It has been in production
+in thousands (millions?) of deployments and is fairly battle-hardened.
+New additions will be met with skepticism. If you think there is a 
+missing feature, please file a bug clearly describing the problem and 
+the alternatives you tried before submitting a PR.
+
+# Reporting security issues
+
+Please DO NOT file a public issue, instead send your report privately to
+security@opencontainers.org.
+
+The maintainers take security seriously. If you discover a security issue,
+please bring it to their attention right away!
+
+If you are reporting a security issue, do not create an issue or file a pull
+request on GitHub. Instead, disclose the issue responsibly by sending an email
+to security@opencontainers.org (which is inhabited only by the maintainers of
+the various OCI projects).
+
+# Copyright and license
+
+Copyright © 2016 Docker, Inc. All rights reserved, except as follows. Code is released under the [Apache 2.0 license](LICENSE.code). This `README.md` file and the [`CONTRIBUTING.md`](CONTRIBUTING.md) file are licensed under the Creative Commons Attribution 4.0 International License under the terms and conditions set forth in the file [`LICENSE.docs`](LICENSE.docs). You may obtain a duplicate copy of the same license, titled CC BY-SA 4.0, at http://creativecommons.org/licenses/by-sa/4.0/.