[domino] log when it's impossible to get a connection to the web service

extra/modules/abelium_domino_synchro.py

@@ -18,6 +18,9 @@ def synchronize_domino(publisher):
     if not is_activated(publisher) or not regie:
         return
     client = get_client(publisher)
+    if client is None:
+        logger.warning('Unable to create a DominoWS object')
+        return
     client.clear_cache()
     users = User.values()
     users_by_mail = dict(((user.email, user) for user in users))