`rake gitlab:cleanup:repos` will remove all hashed-storage repositories

From: https://gitlab.com/gitlab-com/infrastructure/issues/2821#note_47684308

In %10.0 we introduced "hashed storage". When enabled, rather than storing projects on disk in a location determined by project.full_path, they are now stored in @hashed/aa/bb/full-hash. The hash is generated by SHAing the project ID.

The use of full_path needs to be re-evaluated and tested.

# `rake gitlab:cleanup:repos` will remove all hashed-storage repositories
lib/tasks/gitlab/cleanup.rake:91:            next if Project.find_by_full_path(repo_with_namespace)