NETFLIX-BUILD: Fix pyspark rdd.materialize.

Materialize is not in the Java API, so pyspark needs to call the method
on the underlying Scala RDD.

python/pyspark/rdd.py

@@ -257,7 +257,7 @@ def materialize(self):
         """
         Action to force materialization of this RDD. Returns a new RDD.
         """
-        return RDD(self._jrdd.materialize(), self.ctx,
+        return RDD(self._jrdd.rdd().materialize(), self.ctx,
             self._jrdd_deserializer)
 
     def checkpoint(self):