Fix the `gitlab:gitlab_shell:check` task

What does this MR do?

This change the gitlab:gitlab_shell:check task to check that the repositories storage path are owned by the root group

Why was this MR needed?

This fixes an issue where we'd check that the repositories storage path are owned by the GitLab Shell owner group, but the group is actually set to root on purpose "since the beginning of time", see https://gitlab.com/gitlab-org/omnibus-gitlab/merge_requests/1331#note_27278122.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Fixes omnibus-gitlab#1993 (closed).