Add pbr and hacking to gerrit.

Change-Id: I2a9030e8116c05947aad85f54520b851de326a29
Reviewed-on: https://review.openstack.org/24970
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins