ensure no code merges to tempest/tests

because of the restructure, we've had past merges coming into
tempest/tests. Put a check in to stop this for safety. We can
pull it at havana release safely, but it will help us on reviews
during the rest of the cycle.

Change-Id: I0714cd6f06bb89660fb121ca2394a89fc0ee9cb5
1 file changed