Add upload to Google Cloud Storage and Google Compute Image creation

- the image upload uses the cloud API
- currently auth and image creation need the `gcloud` CLI tool.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

vendor/golang.org/x/oauth2/google/appengineflex_hook.go

@@ -0,0 +1,11 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build appenginevm
+
+package google
+
+func init() {
+	appengineFlex = true // Flex doesn't support appengine.AccessToken; depend on metadata server.
+}