test(utils): fix flaky SIGTERM-ignored terminate test (bash tail-exec)

[CMGS]

The test job on master (7e4406f) failed with a 120s package timeout in utils, hung on TestTerminateProcess_SIGTERMIgnored_FallsBackToKill (58s in). A rerun passed — it is flaky, not a regression, and not caused by #80 (which only added two fast pure-function tests to the package).

Root cause

The helper process bash -c ""trap "" TERM; sleep 60"" gets tail-exec-optimized by bash: with sleep as the last command, bash execs it in place, so /proc/<pid>/cmdline argv0 becomes sleep, not bash. Verified on ubuntu 24.04 bash 5.2.21 (the CI image) and bash 5.3.

TerminateProcess(pid, "bash", "sleep", …) calls VerifyProcessCmdline, which requires filepath.Base(argv0) == "bash" before it will signal. It is a startup race: cmd.Start() forks bash, which then takes a few ms to exec into sleep.

• Usually the cmdline check reads bash … before the exec lands → check passes → SIGTERM (trapped) → grace → SIGKILL → fast pass.
• Occasionally the exec wins → cmdline is sleep → check fails → TerminateProcess no-ops → the undead sleep 60 runs its full 60s → the test blocks on cmd.Wait() → the utils package exceeds its 120s -timeout.

(macOS never hit this: verifyProcessCmdline returns errVerifyUnsupported there, so VerifyProcessCmdline falls back to IsProcessAlive and always proceeds.)

Fix

Append ; : so sleep is no longer the last command and bash cannot tail-exec — the process stays resident as bash, keeping argv0 stable. This is the same guard TestFindVMMByCmdline already uses (sleep 60 && :). Production TerminateProcess callers pass real binaries (cloud-hypervisor) that never rename themselves, so only the test was affected.

Verification

• ubuntu 24.04 bash 5.2.21: old command → cmdline sleep 60; fixed command → cmdline bash -c ... (argv0 stays bash).
• Fixed test on real Linux (go 1.26, pidfd path) under -race, 50 iterations: all pass, no hang (181s total, uniform — a single flake hit would have added a ~60s outlier).
• Local: build, make lint (linux+darwin, 0 issues), golangci-lint fmt --diff clean.