Adds an unset_rugged rake task that unsets all rugged feature flags.
Also fixes the existing disable_rugged task to have it explicitly
disable feature flags instead of just unsetting them.
This brings back some of the changes in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20339.
For users using Gitaly on top of NFS, accessing the Git data directly
via Rugged is more performant than Gitaly. This merge request introduces
the feature flag `rugged_find_commit` to activate Rugged paths.
There are also Rake tasks `gitlab:features:enable_rugged` and
`gitlab:features:disable_rugged` to enable/disable these feature
flags altogether.
Part of four Rugged changes identified in
https://gitlab.com/gitlab-org/gitlab-ce/issues/57317.
