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/NYTimes/gziphandler/gzip_go18.go

@@ -0,0 +1,43 @@
+// +build go1.8
+
+package gziphandler
+
+import "net/http"
+
+// Push initiates an HTTP/2 server push.
+// Push returns ErrNotSupported if the client has disabled push or if push
+// is not supported on the underlying connection.
+func (w *GzipResponseWriter) Push(target string, opts *http.PushOptions) error {
+	pusher, ok := w.ResponseWriter.(http.Pusher)
+	if ok && pusher != nil {
+		return pusher.Push(target, setAcceptEncodingForPushOptions(opts))
+	}
+	return http.ErrNotSupported
+}
+
+// setAcceptEncodingForPushOptions sets "Accept-Encoding" : "gzip" for PushOptions without overriding existing headers.
+func setAcceptEncodingForPushOptions(opts *http.PushOptions) *http.PushOptions {
+
+	if opts == nil {
+		opts = &http.PushOptions{
+			Header: http.Header{
+				acceptEncoding: []string{"gzip"},
+			},
+		}
+		return opts
+	}
+
+	if opts.Header == nil {
+		opts.Header = http.Header{
+			acceptEncoding: []string{"gzip"},
+		}
+		return opts
+	}
+
+	if encoding := opts.Header.Get(acceptEncoding); encoding == "" {
+		opts.Header.Add(acceptEncoding, "gzip")
+		return opts
+	}
+
+	return opts
+}