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.

Change-Id: Ibb1b0159ca8267ce3ab6ffb1752ab10ddb4b8139

handlers/main.yml

@@ -30,6 +30,7 @@
   listen:
     - "Restart ceilometer services"
     - "venv changed"
+    - "systemd service changed"
 
 - name: Start services
   service:
@@ -48,3 +49,4 @@
   listen:
     - "Restart ceilometer services"
     - "venv changed"
+    - "systemd service changed"

tasks/main.yml

@@ -80,7 +80,12 @@
       {% set services = [] %}
       {% for service in ceilometer_services.values() %}
       {%   if service.group | intersect(group_names) %}
-      {%     set _ = service.update({'enabled': 'yes', 'state': 'started'}) %}
+      {%     set _ = service.update(
+                {
+                  'enabled': value['enabled'] | default(True),
+                  'state': value['state'] | default('started')
+                }
+              ) %}
       {%     set _ = service.pop('group') %}
       {%     set _ = services.append(service) %}
       {%   endif %}