the weird condition in the code 
causes the task to end with double exception, hard
to understand what really had happened. 

 
producing output like that:


|    i am task..
|    i keep working
|    Exception in callback Task._step()
|    handle: <Handle Task._step()>
|    Traceback (most recent call last):
|      File "/home/http/Python-3.5.0/lib/python3.5/asyncio/tasks.py", line 239, in _step
|        result = coro.send(value)
|    StopIteration
|
|    During handling of the above exception, another exception occurred:
|
|    Traceback (most recent call last):
|      File "/home/http/Python-3.5.0/lib/python3.5/asyncio/events.py", line 125, in _run
|        self._callback(*self._args)
|      File "/home/http/Python-3.5.0/lib/python3.5/asyncio/tasks.py", line 241, in _step
|        self.set_result(exc.value)
|      File "/home/http/Python-3.5.0/lib/python3.5/asyncio/futures.py", line 335, in set_result
|        raise InvalidStateError('{}: {!r}'.format(self._state, self))
|    asyncio.futures.InvalidStateError: FINISHED: <Task finished coro=<task() done, defined at test_aio_exception.py:4> exception=RuntimeError('something bad',)>


it would be good to improve that shutdown procedure 
to pinpoint real reason why and when it got into broken state.

additional info can be found here:
https://groups.google.com/forum/#!topic/python-tulip/-EcYtJXDvSo