sync docker-registry with upstream

[proppy]

And import https://github.com/dmp42/docker-registry-driver-gcs

[proppy]

After discussing with @dmp42 on https://botbot.me/freenode/google-containers/2014-09-18/?msg=21908948&page=8 the plan is the following:

• [x] branch the repo
• [x] delete the registry tree
• [x] copy the plugin from https://github.com/dmp42/docker-registry-driver-gcs
• [x] pip install the stable version of the registry in the Dockerfile
• [x] add the plugin and modify the ENTRYPOINT to enable the gcs plugin

[bshi]

@proppy any update on this? #22 is biting us pretty badly - I'm happy to jump in and help too.

[proppy]

@bshi sorry to let that slip, will take a stab at it next week. I can definitely use some help for testing. Thanks!