pytest hangs rather than exits if monitoring `router_starter` fails with an exception

[benclifford]

Describe the bug

With
pytest parsl/tests/ --config parsl/tests/configs/htex_local_alternate.py --log-cli-level=ERROR

If monitoring router_starter and dbm_starter raise an exception, so their respective processes end, the main thread of this test then hangs. I think it's likely that this also happens for real users, but I haven't tried to reproduce this outside of pytest.

To Reproduce

Make these processes exit at startup by adding a deliberate exception.

Expected behavior
The test run should terminate as a failure, not hang.

Environment
My dev laptop, lightly modified 1c7a0e4