PR #30136 CI: test_dockerfile_entrypoint_routes_through_the_init failed
because the test hardcoded known_inits = ('tini', 'dumb-init',
'catatonit'). The PR replaced tini with s6-overlay's /init (which execs
s6-svscan as PID 1) — same SIGCHLD-reaping contract, different name,
so the substring scan against ENTRYPOINT missed it.
Two-part fix:
1. Extend the accepted token list to include 's6-overlay', 's6-svscan',
and '/init'. The contract these tests enforce is behavioural ('some
PID-1 init reaps SIGCHLD'), so the names list is purely a recognition
table and any reaper-capable family should qualify.
2. Harden test_dockerfile_installs_an_init_for_zombie_reaping (the
sibling check) against comment-only matches. It was scanning the full
Dockerfile text and only passed because the word 'tini' is still in
a historical comment explaining why we used to use it. The next
person to clean up that comment would have silently broken the test.
New _instruction_text() helper joins only the parsed, non-comment
Dockerfile instructions so stale comments can't satisfy the check.
(cherry picked from commit ffc1bb6393e024f18aeab537628c4e01747c89fc)
7d54288d82