Dask Jobqueue is not async ready

[guillaumeeb]

See discussions in #565.

In particular https://github.com/dask/dask-jobqueue/pull/565#pullrequestreview-1052591018.

It is not safe to create a ProcessInterface without a running loop. Use of the default event loop is deprecated in Python. We have to make sure we are ready for the removal and support running with multiple calls to asyncio.run.

cc @graingert who already thought about it.