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-DUT102-8

@anew : Please review. Thanks.
I don't like this error message. Because it assumes that trySetDecoder() only supports bytes and text. If we ever change trySetDecoder(), this message will be wrong. The message (or the set of supported types) must be provided by StreamInputFormat.