Add efficacy indicators for workload_stabilization strategy

This patch set adds efficacy indicators for workload_balancing
goal (that includes workload_stabilization and workload_balance
strategies so far).

Change-Id: I5b04d084ace7c661001c62f07b8308e5763e144d

watcher/decision_engine/goal/efficacy/base.py

@@ -72,7 +72,8 @@ class EfficacySpecification(object):
         }
         for indicator in self.indicators_specs:
             schema["properties"][indicator.name] = indicator.schema
-            schema["required"].append(indicator.name)
+            if indicator.required:
+                schema["required"].append(indicator.name)
         return schema
 
     def validate_efficacy_indicators(self, indicators_map):