[Trivial fix] Do not use self in classmethod

Do not use self in classmethod, cls should be used instead.

Change-Id: Ib4e5b27e237122e519bdf84d2af1e8c0ea5f1dda

watcher/decision_engine/scoring/dummy_scoring_container.py

@@ -37,7 +37,7 @@ class DummyScoringContainer(base.ScoringEngineContainer):
     """
 
     @classmethod
-    def get_scoring_engine_list(self):
+    def get_scoring_engine_list(cls):
         return [
             SimpleFunctionScorer(
                 'dummy_min_scorer',