Move to standardised fork-hooks that we can use with Puma and Unicorn
Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/3592
See related merge requests:
- https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22372
- https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/7943
- gitlab-development-kit!532 (merged)
Please note that https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22372, https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/7943 and this MR should all be merged concurrently.