RnaSeqDgeExample: fixed error and added unit tests
- RnaSeqDgeExample: fixed an error in the runExample method: result is initialized to false, switched from the workflow engine factory to the workflow factory.
- HistogramExampleTest: clear the dummy workflow flags before each test; the tests could fail depending on the execution order.
- RnaSeqDgeExampleTest: clear the dummy workflow flags before each test, added two more unit tests.
- DummyWorkflow: moved custom dummy output creation from the run method to the RnaSeqDgeExampleTest.addDummyOutput method, added a clear method to clear the special result and exception flags.