Enable OAuth 2.0 when using Google Cloud Storage as a Storage for
docker-registry.
rm self.
add oauth2 option to the config, merge both gcs flavors together.
Disable pyflake unused import warning
Switch to using gcloud util.
Update the doc
Merge branch 'master' of https://github.com/ktintc/docker-registry

Conflicts:
	config/config_sample.yml