PyUnit test runner does not yet work with interactive mode

[ryan-collingham]

As expected - the PyUnit test runner does not yet work with interactive test runner. It needs to implement both dry_run() and run_testcases_iter() methods correctly to work with interactive mode.:

Current behaviour: exception raised on setup, looks like dry_run() is implemented on the PyUnit runner but is not returning the expected type:

Starting TestRunner[PyUnit] in interactive mode
Traceback (most recent call last):
  File "C:\Users\Ryan\Documents\code\testplan\testplan\common\entity\base.py", line 861, in run
    self._ihandler = self.cfg.interactive_handler(
  File "C:\Users\Ryan\Documents\code\testplan\testplan\runnable\interactive\base.py", line 61, in __init__
    self.report = self._initial_report()
  File "C:\Users\Ryan\Documents\code\testplan\testplan\runnable\interactive\base.py", line 675, in _initial_report
    test_report = test.dry_run().report
AttributeError: 'TestGroupReport' object has no attribute 'report'