Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Fixes #2870 (closed).
@marin Don't worry about adding this to omnibus yet, I'll be moving all of the mail_room configuration to config/gitlab.yml so that source installation users don't need to edit config/mail_room.yml which contains a lot of stuff they shouldn't touch. See https://github.com/tpitale/mail_room/pull/53.