Spark now uses configure style

- Spark uses configurer style API : CDAP-382

Build running here: https://builds.cask.co/browse/CDAP-DUT316-2

This opens two more related (but independent to this merge) issues: 
CDAP-989: Doc changes for the Spark configurer style API
CDAP-990: Apps and Guide changes to use Spark configurer style API
Because this is the user program class which we pass to spark when will call its main function.
So, we take the class name. We can take the class and while calling spark main function pass its name. 
Do you think that will be better ?