Add topic parameter to notify callback call to avoid exception

Change-Id: Iedf9ee36d4a135b3ff0f51e65c96c83a855d88bc

dragonflow/db/drivers/etcd_db_driver.py

@@ -179,10 +179,10 @@ class EtcdDbDriver(db_api.DbApi):
                                          timeout=5)
                 keys = entry.key.split('/')
                 self.notify_callback(keys[1], keys[2], entry.action,
-                                     entry.value)
+                                     entry.value, None)
                 self.current_key = entry.modifiedIndex + 1
             except Exception as e:
                 if "Read timed out" not in e.message:
                     LOG.warning(e)
                 self.notify_callback(None, None, 'sync',
-                                     None)
+                                     None, None)