event loop: Use the event loop provided by pytest-asyncio
event loop: Use the event loop provided by pytest-asyncio

If @pytest.mark.asyncio decorator is used for test methods, the event loop of
pytest-asyncio is set as the default asyncio event loop automatically.

ZKClient was initiated without the loop argument and was called while not
inside the @pytest.mark.asyncio decorator, so it uses the default asyncio event
loop.

Hence, plenty of tests complained that "Future attached to a different loop".

To solve this problem, make ZKClient use event_loop generated by pytest-asyncio
instead of default asyncio event loop.

tipsi/aiozk,tipsi/aiozk