Execute system hooks after-commit when executing project hooks
Backports part of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/4229, and fixes another bug.
Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/42294
Backports part of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/4229, and fixes another bug.
Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/42294