We stop relying on Gitlab::Git::Env for the RevList class, and use
Gitlab::Git::Repository#run_git methods inteaad. The refactor also fixes
another issue, since we now top using "path_to_repo" (which is a
Repository model method).

Replaces all the explicit include metadata syntax in the specs (tag:
true) into the implicit one (:tag).
Added a cop to prevent future errors and handle autocorrection.

This allows the current Gitaly migration to depend on less code outside
of the Gitlab::Git module

Remove superfluous lib: true, type: redis, service: true, models: true, services: true, no_db: true, api: true
Signed-off-by: NRémy Coutable <remy@rymai.me>

- Ignore JS fixtures
- Ignore qa directory
- Rewrite concern specs to put concern name first

Previously, we were calling out to `popen` without asserting on the returned
exit-code. Now we raise a `RuntimeError` if the exit code is non-zero.