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: I5ba33177a121d75e92a929e5bd81cfd4872ef406

handlers/main.yml

@@ -30,4 +30,4 @@
   listen:
     - "Restart trove services"
     - "venv changed"
-
+    - "systemd service changed"

vars/main.yml

@@ -23,7 +23,14 @@ filtered_trove_services: |-
           (('condition' not in value) or
            ('condition' in value and value['condition'])) and
             not ('wsgi_app' in value and value['wsgi_app']) %}
-  {%     set _ = value.update({'service_key': key}) %}
+  {%     set _ = value.update(
+            {
+              'service_key': key,
+              'enabled': value['enabled'] | default(True),
+              'state': value['state'] | default('started')
+            }
+          )
+  %}
   {%     set _ = services.append(value) %}
   {%   endif %}
   {% endfor %}