Workers left alive on MOM node

**Describe the bug**
Workers are not cleaned up from a launch node after a job is terminated by the schedular.

My app places the FuncX manager on the MOM node of a Cray supercomputer so that workers can launch MPI applications via system calls. The manager process is killed when the job exits but the workers stay afterwards.

Looking at the logs, I note the workers report receiving a Signal 15 but do not exit. Is that expected?

```
(miniconda-3/latest//home/lward/exalearn/edw/env) lward@thetalogin6:~/.funcx/nwchem/HighThroughputExecutor/worker_logs/70f647195873> more funcx_worker_32.log
1649883351.811096 2022-04-13 20:55:51 INFO MainProcess-70029 MainThread-140634291058496 funcx_endpoint.executors.high_throughput.funcx_worker:85 __init__ Initializing worker 32
1649883351.813936 2022-04-13 20:55:51 INFO MainProcess-70029 MainThread-140634291058496 funcx_endpoint.executors.high_throughput.funcx_worker:86 __init__ Worker is of type: RAW
1649883351.814639 2022-04-13 20:55:51 INFO MainProcess-70029 MainThread-140634291058496 funcx_endpoint.executors.high_throughput.funcx_worker:95 __init__ Trying to connect to : tcp://127.0.0.1:52075
1649883351.815704 2022-04-13 20:55:51 INFO MainProcess-70029 MainThread-140634291058496 funcx_endpoint.executors.high_throughput.funcx_worker:109 start Starting worker
1649884526.686283 2022-04-13 21:15:26 ERROR MainProcess-70029 MainThread-140634291058496 funcx_endpoint.executors.high_throughput.funcx_worker:101 handler Signal handler called with signal 15
1649884762.299373 2022-04-13 21:19:22 ERROR MainProcess-70029 MainThread-140634291058496 funcx_endpoint.executors.high_throughput.funcx_worker:101 handler Signal handler called with signal 15
```

**To Reproduce**
TBD. My app has a complex set up, but I can create a minimal example on request.

**Expected behavior**
Everything dies when Cobalt commands it.

**Environment**
- OS: CentOS
- OS & Container technology: None
- Python version @ 3.8.12

- Python version @ 3.8.12
- funcx version @ 58493f
- funcx-endpoint version @ 58493f

**Distributed Environment**
- Where are you running the funcX script from? Login node
- Where does the endpoint run? Login node
- What is your endpoint-uuid? ff59d7d1-e2f5-4a38-8bb8-ba6de588c7c7
- Attach endpoint logs at `~/.funcx/` if this is an endpoint issue.
Please let us know if you'd prefer to share logs privately.

[worker-no-die.tar.gz](https://github.com/funcx-faas/funcX/files/8484810/worker-no-die.tar.gz)

Start with funcx_endpoint.executors.high_throughput.funcx_worker and the worker log showing repeated Signal 15 handling. Reproduce the worker cleanup behavior in a minimal setup, then verify that workers exit when the manager job is terminated by Cobalt.

Written by the indexing model from the issue text.