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)

For completeness's sake, maybe we should have a PYSPARK_SKIP_TESTS, too.  This will probably be moot after my planned refactoring, though.