Updated Streaming tests

Major changes are as follows:
- Added more tests - updateStateByKey, GroupByKeyAndWindow, ReduceByKeyAndWindow
- Updated config and main run script to make it easier to disable tests of certain modules, without having comments the tests of those modules one-by-one (maybe I should consider uncommenting all the tests, and use the variables to disable them by default)

Not a merge-blocker, but it might be nice to leave comments at the top of files that we've backported from newer versions of Spark, such as this file; this could help future readers, etc.