Fix 500 error for Group#web_url method if nested group
Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/2772
No changelog needed because users are not affected by it yet.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/2772
No changelog needed because users are not affected by it yet.