Get planner from solution

support Strategy select different planner
Implements: bp watcher-planner-selector

Change-Id: I586e67f782e2965234826634ba3ff51681af4df8

watcher/decision_engine/solution/base.py

@@ -72,7 +72,7 @@ class BaseSolution(object):
         :type strategy: :py:class:`~.BaseStrategy` instance
         """
         self.goal = goal
-        self.strategy = strategy
+        self._strategy = strategy
         self.origin = None
         self.model = None
         self.efficacy = efficacy.Efficacy(self.goal, self.strategy)
@@ -85,6 +85,10 @@ class BaseSolution(object):
     def efficacy_indicators(self):
         return self.efficacy.indicators
 
+    @property
+    def strategy(self):
+        return self._strategy
+
     def compute_global_efficacy(self):
         """Compute the global efficacy given a map of efficacy indicators"""
         self.efficacy.compute_global_efficacy()