When action plan is empty, its state is incorrect

When the action plan is empty,its state is still 'RECOMMENDED'.
I think it's should be 'SUCCEED'.
Closes-Bug: #1619155

Change-Id: Icd10707c7892089999f8b37775ca62bde47db0c4

watcher/decision_engine/planner/default.py

@@ -94,6 +94,7 @@ class DefaultPlanner(base.BasePlanner):
         if len(scheduled) == 0:
             LOG.warning(_LW("The action plan is empty"))
             action_plan.first_action_id = None
+            action_plan.state = objects.action_plan.State.SUCCEEDED
             action_plan.save()
         else:
             # create the first action