Tweaks to make install run idempotent

roles/keystone/templates/keystone.service

@@ -12,7 +12,7 @@ ExecStart=/usr/bin/docker run --name %n \
   -e "KEYSTONE_HOST={{ hostvars[groups['keystone'][0]]['ansible_default_ipv4']['address'] }}" \
   -p 5000:5000 -p 35357:35357 \
   -v /srv/keystone/fernet-keys:/etc/keystone/fernet-keys \
-  hpc/openstack-keystone
+  {{ docker_image }}
 
 [Install]
 WantedBy=multi-user.target