Changes to enable eu-central-1.

Fixes https://github.com/docker/docker-registry/issues/674 https://github.com/docker/docker-registry/issues/661 and other eu-central-1 related issues.

Please rather change this https://github.com/docker/docker-registry/blob/master/depends/docker-registry-core/setup.py#L38 to unconditionnally install simplejson (or better, remove it from the setup.py and add it to https://github.com/docker/docker-registry/blob/master/depends/docker-registry-core/requirements/main.txt)