Spark Integration: SparkPageRank example now reads directly from Stream

I am opening this PR against feature/spark-streams as I am waiting for the build to pass here before I merge it to develop and want to get this out to develop. 

https://builds.cask.co/browse/CDAP-DUT102-13

This will also be merged to develop. 


This also need documentation changes. I am working on that and will open a new PR for that.