Log CDM structure before+after executing strategy

In this changeset, I added debug logs to dump the cluster data model
copy structure (as XML) before and after the execution of the strategy.

By doing so, we can see the cluster data model structure that is
expected after the execution of the corresponding action plan.

Change-Id: I81c23e148a78d9b176154f7620087a322a5bce28

watcher/decision_engine/strategy/strategies/outlet_temp_control.py

@@ -230,6 +230,8 @@ class OutletTempControl(base.ThermalOptimizationBaseStrategy):
         if not self.compute_model:
             raise wexc.ClusterStateNotDefined()
 
+        LOG.debug(self.compute_model.to_string())
+
     def do_execute(self):
         # the migration plan will be triggered when the outlet temperature
         # reaches threshold
@@ -284,3 +286,5 @@ class OutletTempControl(base.ThermalOptimizationBaseStrategy):
     def post_execute(self):
         self.solution.model = self.compute_model
         # TODO(v-francoise): Add the indicators to the solution
+
+        LOG.debug(self.compute_model.to_string())