By default, --prune is added to the command-line of a `git fetch` operation,
but for repositories with many references this can take a long time to run. We
shouldn't need to run --prune the first time we fetch a new repository.
Migration is done through a small refactoring, which makes us call
endpoins which are performing the same actions for namespaces.
Tests are added to ensure only the project is removed that should be
removed.
Closesgitlab-org/gitaly#873
By importing this Ruby code into gitlab-rails (and gitaly-ruby), we avoid
200ms of startup time for each gitlab_projects subprocess we are eliminating.
By not having a gitlab_projects subprocess between gitlab-rails / sidekiq and
any git subprocesses (e.g. for fork_project, fetch_remote, etc, calls), we can
also manage these git processes more cleanly, and avoid sending SIGKILL to them
