Returns a Java StorageLevel based on a pyspark.StorageLevel.

def _getJavaStorageLevel(self, storageLevel):
        """
        Returns a Java StorageLevel based on a pyspark.StorageLevel.
        """
        if not isinstance(storageLevel, StorageLevel):
            raise Exception("storageLevel must be of type pyspark.StorageLevel")

        newStorageLevel = self._jvm.org.apache.spark.storage.StorageLevel
        return newStorageLevel(storageLevel.useDisk,
                               storageLevel.useMemory,
                               storageLevel.useOffHeap,
                               storageLevel.deserialized,
                               storageLevel.replication)