Spark Integration: Streams support for Spark Jobs

Adds support to read Streams in Spark to resolve : CDAP-403

Build Running: https://builds.cask.co/browse/CDAP-DUT102-4

@anew : Please review. Thanks.
This get sets when we create a new StreamBatchReadable. 

SparkContext provides two interface one which takes decoderType and one which does not.