Make version of tempest configurable
Make version of tempest configurable

This patch makes tempest version configurable so we can override
it in CI for DLRN promotion jobs for stable branches.

There have been some backwards incompatible changes in tempest
and ceilometer ( https://review.openstack.org/#/c/395506/ ) not
tagged yet in stable/newton. In order to get p-o-i pass with this
commits we need to use an updated version of tempest.

Change-Id: Ifb37a5a3a809c8a94d055d9cdc2b880e1ec9a115

openstack/puppet-openstack-integration,openstack/puppet-openstack-integration,openstack/puppet-openstack-integration