Fix glance config copy when a service is disabled

In this patch, the glance-registry service was disabled:
https://review.openstack.org/#/c/566804/

However, the config task still tries to copy files for it, which will
break due to path errors.

Change-Id: If39bb12bf830e6559342037ae2a2b99a784ee503

ansible/roles/glance/tasks/config.yml

@@ -106,6 +106,7 @@
   when:
     - glance_policy_file is defined
     - inventory_hostname in groups[item.value.group]
+    - item.value.enabled | bool
   with_dict: "{{ glance_services }}"
   notify:
     - Restart glance-api container