Add .gitreview file.

Change-Id: I5a8b581b88733e7096fa5e1288f589099244b34e
Reviewed-on: https://review.openstack.org/33458
Approved: Thierry Carrez <thierry@openstack.org>
Reviewed-by: Thierry Carrez <thierry@openstack.org>
Tested-by: Jenkins