Unit test cleanup and bugfix.

ForwardingTest.testForwardDeleteFlowsByDescriptorMultiple() passed in Eclipse, but failed when run by "ant test".
Changed Forwarding.deleteFlowsByDescriptor() to use List<> instead of Set<> to simplify the unit test.
Tests now pass in every configuration I'm able to run them (eclipse single test, eclipse test class, eclipse all tests, ant all tests).

Also general code and comment cleanup.