Add back in git commit message checking.

Change-Id: If608a117b9584c1138b5fbbdd56599922bdfa49e
Reviewed-on: https://review.openstack.org/28219
Reviewed-by: Joe Gordon <jogo@cloudscaling.com>
Approved: Sean Dague <sean@dague.net>
Reviewed-by: Sean Dague <sean@dague.net>
Tested-by: Jenkins