Why are these changes needed?

This makes unittest logs easier to read which can reduce iteration time.

The GPU one should be uncontroversial.

I added a wait after forcibly killing a subprocess; this doesn't guarantee that the ResourceWarning goes away, but it fixed it for me. Might be better to change the subprocess so it responds to SIGTERM more quickly, but that would take more effort.

The remaining changes close log files after passing them to subprocesses. I noticed a comment on #10279 which claims that they were kept open deliberately. It's possible that I'm missing something, but I think the files are only used by these subprocesses, and most OSs I'm aware of will keep file descriptors open in child processes after the parent closes them. In any case subprocess.Popen duplicates these handles before passing them to the child on POSIX [1] and Windows [2].

[1] https://github.com/python/cpython/blob/07119dd38c9a6e5da84ca8a0a46acdf8a3e60ecf/Lib/subprocess.py#L1541
[2] https://github.com/python/cpython/blob/07119dd38c9a6e5da84ca8a0a46acdf8a3e60ecf/Lib/subprocess.py#L1208

Related issue number

Closes #9546 and #10279.

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(