avahi: Split app initialization

Tests:

- After startup, names module shows a .local domain if app is enabled.

- If app is disabled, .local domain is not shown.

- When hostname is changed, .local domain name in names modules changes.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/avahi/__init__.py

@@ -85,6 +85,8 @@ class AvahiApp(app_module.App):
                                        **manifest.backup)
         self.add(backup_restore)
 
+    def post_init(self):
+        """Perform post initialization operations."""
         if self.is_enabled():
             domain_added.send_robust(sender='avahi',
                                      domain_type='domain-type-local',