MNT: if we have exception coming out of durring_task fail harder
MNT: if we have exception coming out of durring_task fail harder

Calling `self._task_fut.cancel()` does not guarantee that the `_run`
loop will actually stop and could continue to run in the
background (!!).  Use `halt` instead.

ericdill/bluesky,ericdill/bluesky