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: I3f17e680d1bf9e6e34de6b611db2a484eabbded9

handlers/main.yml

@@ -22,3 +22,4 @@
   when: inventory_hostname in groups[item.value.group]
   listen:
     - "venv changed"
+    - "systemd service changed"

tasks/main.yml

@@ -116,7 +116,12 @@
       {% set services = [] %}
       {% for service in masakari_services.values() %}
       {%   if service.group in group_names %}
-      {%     set _ = service.update({'enabled': 'yes', 'state': 'started'}) %}
+      {%     set _ = service.update(
+              {
+                'enabled': service['enabled'] | default(True),
+                'state': service['state'] | default('started')
+              }
+          ) %}
       {%     set _ = service.pop('group') %}
       {%     set _ = services.append(service) %}
       {%   endif %}