Client Preparation: Prepare GitLab-EE for Internal Mirroring

~Conversation: #554 (closed)

From #554 (comment 40224657), @jacobvosmaer-gitlab wrote:

• EE: refactor https://gitlab.com/gitlab-org/gitlab-ee/blob/master/app/services/projects/update_repository_storage_service.rb to use git remotes and mirroring instead of gitlab-projects mv-storage. This will use the Gitlab::Git::Repository#fetch(remote) function added in the previous step.