Spark Integration: Close spark context in unit test

SparkContext is messed up thing. 
Apache Spark says to close the context at the end of job which happen automatically most of the time because the program finishes. 

During the release the SparkProgramRunner tests were also failing sometimes randomly and the two changes which we did was. 
1. According to your suggestion, create a new temp dir for the test runs. 
2. Close the context manually. 

From then the the ProgramRunner test has never failed.

I want to see if this fixes it here too. Since the build always pass on feature branch the only way to test out it to merge
https://builds.cask.co/browse/CDAP-DUT102