[multiple-commpaths] Allows colon-separated commpath list

[rountree]

Per-server selection, first path in --commpaths that works for that server gets picked. No consensus process, as the commpath is not visible outside of the server and its particular clients.

[mplegendre]

@rountree - Are you working on fixing the CI failures?

[rountree]

@mplegendre Yes. What's queued up for this coming Friday is:

1. A PR adding workflows for granular resource manager testing and log recovery via artifacts.
2. A FAQ on how to launch GitHub workflows, monitor progress, and download artifacts all via the command line.
3. A PR with most of the low-hanging-fruit configure file changes.
4. A patched multiple-commpaths PR that passes repeated invocations of the existing ci.yml workflow.

[rountree]

Debugging notes:

Running bd856fa (tip of multiple-commpaths at the moment)
3/13 ci.yml failures
a) Flux, Running: ./run_driver --dependency --push, Error: The operation was canceled. 17m 27s, 31038941417
b) slurm-rshlaunch, SOME TESTS FAILED (no failures logged), 2m 9s, 31038944077
c) slurm-srun, SOME TESTS FAILED (no failures logged), 1m 18s, 31038929449

Running c0170276 (tip of devel)
3/31 ci.yml
a) Flux, Running: ./run_driver --dependency --push, Error: The operation was canceled., 17m 7s, 31043385441
b) ditto
c) ditto

Running bd856fa (multiple-commpaths)
0/31 ci-slum-srun-artifacts failures
0/31 ci-slurm-artifacts failures

---

Running bd856fa (multiple-commpaths)
4/13 ci.yml failures, 3 Flux, 1 Run spindle-slurm-ubuntu testsuite

---

Running c0445ae (testing-multiple-commpaths)
Run 31106514887 job 92632975191 "Slurm srun, Ubuntu"

At this point GitHub actions became unusably slow.

The good news is that the podman port can replicate the problem on rzadams with a 4% failure rate.