Specific exception for stale cluster state was added.

Specific exception should be thrown when cluster state
is stale. Current usage is to raise this exception if
compute_model.state is True.
Bug was describeid by Jean-Emile DARTOIS.

Change-Id: Iaddb4cc8007c51bb14759c9da829751e834499d0
Closes-Bug: #1621855

watcher/decision_engine/strategy/strategies/basic_consolidation.py

@@ -384,12 +384,16 @@ class BasicConsolidation(base.ServerConsolidationBaseStrategy):
 
     def pre_execute(self):
         LOG.info(_LI("Initializing Server Consolidation"))
+
         if not self.compute_model:
             raise exception.ClusterStateNotDefined()
 
         if len(self.compute_model.get_all_compute_nodes()) == 0:
             raise exception.ClusterEmpty()
 
+        if self.compute_model.stale:
+            raise exception.ClusterStateStale()
+
         LOG.debug(self.compute_model.to_string())
 
     def do_execute(self):