Make gerrit port configurable.

Change-Id: Idf87910a9f82556f247e0232468f2f883d718f97
Reviewed-on: https://review.openstack.org/33927
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins