Change registration of the qt eventloop after a similar change in IPython

[ccordoba12]

It took me several hours to figure this one out!! After ipython/ipython#10756, you can't run %matplotlib qt5 in any Jupyter client that uses ipykernel because it's broken.

This was reported in spyder-ide/spyder#6091 and I created spyder-ide/spyder#6121 to deal with this problem in our side.

[ccordoba12]

The test errors don't seem related to my work.

[takluyver]

I agree that the failures are not related to this. I've just rerun the tests on master and got the same failure. I'm investigating, but I don't have long today to look at it, so feel free to look into it as well.

[takluyver]

It looks like the error occurs with tornado 5.0a1. @minrk, you've been making fixes related to that - any ideas?

________________________________ test_asyncio_interrupt ________________________________

args = (), kwargs = {}

    def skipper_func(*args, **kwargs):
        """Skipper for normal test functions."""
        if skip_val():
            raise nose.SkipTest(get_msg(f,msg))
        else:
>           return f(*args, **kwargs)

../../.local/lib/python3.6/site-packages/IPython/testing/decorators.py:212: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../.local/lib/python3.6/site-packages/ipykernel/tests/test_eventloop.py:43: in test_asyncio_interrupt
    msg_id, content = execute(async_code, KC)
../../.local/lib/python3.6/site-packages/ipykernel/tests/utils.py:66: in execute
    reply = kc.get_shell_msg(timeout=TIMEOUT)
../../.local/lib/python3.6/site-packages/jupyter_client/client.py:77: in get_shell_msg
    return self.shell_channel.get_msg(*args, **kwargs)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <jupyter_client.blocking.channels.ZMQSocketChannel object at 0x7fd0699d87b8>
block = True, timeout = 15000

    def get_msg(self, block=True, timeout=None):
        """ Gets a message if there is one that is ready. """
        if block:
            if timeout is not None:
                timeout *= 1000  # seconds to ms
            ready = self.socket.poll(timeout)
        else:
            ready = self.socket.poll(timeout=0)
    
        if ready:
            return self._recv()
        else:
>           raise Empty
E           queue.Empty

[minrk]

I opened #294 to pin tornado for tests while we work it out.

This PR should be OK

[ccordoba12]

Thanks Min!

[takluyver]

Reopening to rerun tests.