centos7: stop installing horizon tempest plugin from source
centos7: stop installing horizon tempest plugin from source

RDO now provides the package: https://review.openstack.org/#/c/349462 so
we can use it like other services.

Change-Id: I51d183467c45f5899c823118048854ba48fb7a93

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