Fix reap_process_group sudo fallback passing the process group id as the signal number

[ckarnell]

reap_process_group has two sudo fallbacks for EPERM. The first passes a signal and the pids:

["sudo", "-n", "kill", "-" + str(int(sig))] + [str(p.pid) for p in all_processes_in_the_group]

The second, fourteen lines below, passes the process group id where the signal belongs and names no target at all:

subprocess.check_call(["sudo", "-n", "kill", "-" + str(process_group_id)])

That builds sudo -n kill -4242, which /bin/kill rejects with a usage error and exit 2, so check_call raises CalledProcessError and the process is never signalled. The path needs killpg to fail with ESRCH and then os.kill with EPERM, which is the run_as_user case where the group has already gone but the process has not.

Mocking both errnos and capturing the call:

before: ['sudo', '-n', 'kill', '-4242']
after:  ['sudo', '-n', 'kill', '-15', '4242']

#9202 reported this in 2020 against 1.10.9 and named reap_process_group. It was closed without a fix. The line is unchanged.

The added test fails on current main with ['sudo', '-n', 'kill', '-4242'] != ['sudo', '-n', 'kill', '-15', '4242'] and passes with the change. test_process_utils.py goes from 27 passing to 28. It mocks the signal calls, so it needs no database and carries no db_test marker.

[boring-cyborg]

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