Try migrations on staging.

The migration in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11713 renaming all reserved project/group names should be tested on staging to know how long it will take.

In total 108 projects and 24 namespaces are renamed and moved.

The migration to be run: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11713/diffs#8a69609c4f40600e8de5715cc2ced09a2cadeb28