Celery 3.1.23 requires celerytest tweaks

[twall]

Found a few issues when attempting to run a threaded worker.

• Call to Worker.run() should be replaced by Worker.start(). Likely a change in the Celery Worker API?

• setup_celery_worker seems to override any existing app settings, rather than just updating the ones relevant to threaded operation.

• Celery memory backend has a bug in a base method passed two arguments but the implementation takes one. Workaround:

  from kombu.transport.base import Transport
  Transport.register_with_event_loop = lambda _args, *_kwargs: 1

• Memory broker doesn't seem to work. Haven't tracked this down, currently using an AMQP broker instead.