build: move e2e dependencies into e2e/go.mod

Several packages are only used while running the e2e suite. These
packages are less important to update, as the they can not influence the
final executable that is part of the Ceph-CSI container-image.

By moving these dependencies out of the main Ceph-CSI go.mod, it is
easier to identify if a reported CVE affects Ceph-CSI, or only the
testing (like most of the Kubernetes CVEs).

Signed-off-by: Niels de Vos <ndevos@ibm.com>

e2e/vendor/github.com/modern-go/concurrent/README.md

@@ -0,0 +1,49 @@
+# concurrent
+
+[![Sourcegraph](https://sourcegraph.com/github.com/modern-go/concurrent/-/badge.svg)](https://sourcegraph.com/github.com/modern-go/concurrent?badge)
+[![GoDoc](http://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)](http://godoc.org/github.com/modern-go/concurrent)
+[![Build Status](https://travis-ci.org/modern-go/concurrent.svg?branch=master)](https://travis-ci.org/modern-go/concurrent)
+[![codecov](https://codecov.io/gh/modern-go/concurrent/branch/master/graph/badge.svg)](https://codecov.io/gh/modern-go/concurrent)
+[![rcard](https://goreportcard.com/badge/github.com/modern-go/concurrent)](https://goreportcard.com/report/github.com/modern-go/concurrent)
+[![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://raw.githubusercontent.com/modern-go/concurrent/master/LICENSE)
+
+* concurrent.Map: backport sync.Map for go below 1.9
+* concurrent.Executor: goroutine with explicit ownership and cancellable
+
+# concurrent.Map
+
+because sync.Map is only available in go 1.9, we can use concurrent.Map to make code portable
+
+```go
+m := concurrent.NewMap()
+m.Store("hello", "world")
+elem, found := m.Load("hello")
+// elem will be "world"
+// found will be true
+```
+
+# concurrent.Executor
+
+```go
+executor := concurrent.NewUnboundedExecutor()
+executor.Go(func(ctx context.Context) {
+    everyMillisecond := time.NewTicker(time.Millisecond)
+    for {
+        select {
+        case <-ctx.Done():
+            fmt.Println("goroutine exited")
+            return
+        case <-everyMillisecond.C:
+            // do something
+        }
+    }
+})
+time.Sleep(time.Second)
+executor.StopAndWaitForever()
+fmt.Println("executor stopped")
+```
+
+attach goroutine to executor instance, so that we can
+
+* cancel it by stop the executor with Stop/StopAndWait/StopAndWaitForever
+* handle panic by callback: the default behavior will no longer crash your application