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: Id81230eb8b26f7c666d053d70230149fa93c7822

handlers/main.yml

@@ -21,3 +21,4 @@
   with_items: "{{ filtered_barbican_services }}"
   listen:
     - "venv changed"
+    - "systemd service changed"

vars/main.yml

@@ -30,7 +30,8 @@ filtered_barbican_services: |-
   {%     set _ = value.update(
            {
              'service_key': key,
-             'enabled': 'yes',
+             'enabled': value['enabled'] | default(True),
+             'state': value['state'] | default('started'),
              'config_overrides': value.init_config_overrides
            }
          )