Ensure service is restarted on unit file changes

At the moment we don't restart services if systemd unit file is changed.

We knowingly prevent systemd_service role handlers to execute
by providing `state: started` as otherwise service will be restarted twice.
With that now  we ensure that role handlers will also listen for systemd
unit changes.

Depends-On: https://review.opendev.org/c/openstack/openstack-ansible-os_heat/+/879963
Depends-On: https://review.opendev.org/c/openstack/openstack-ansible/+/880470
Change-Id: I5561693e490700bc572e196e36e8ef0fa4df1ec5

handlers/main.yml

@@ -20,3 +20,4 @@
   when: inventory_hostname in groups[item.group]
   listen:
     - "venv changed"
+    - "systemd service changed"

vars/main.yml

@@ -22,8 +22,8 @@ filtered_sahara_services: |-
   {%     set _ = value.update(
           {
             'service_key': key,
-            'enabled': 'yes',
-            'state': 'started',
+            'enabled': value['enabled'] | default(True),
+            'state': value['state'] | default('started'),
             'config_overrides': value.init_config_overrides
           }
         )