Fix TypeError in function chunkify

This patch fixes TypeError of range() in function chunkify, as
range() integer step argument expected, but got str.

Change-Id: I2acde859e014baa4c4c59caa6f4ea938c7c4c3bf
(cherry picked from commit c717be12a6)

watcher/decision_engine/planner/weight.py

@@ -87,6 +87,7 @@ class WeightPlanner(base.BasePlanner):
     @staticmethod
     def chunkify(lst, n):
         """Yield successive n-sized chunks from lst."""
+        n = int(n)
         if n < 1:
             # Just to make sure the number is valid
             n = 1