Record the node a container is running on, not the container id

[adrpo]

Follow-up to #320, which is merged.

#320 records socket.gethostname() as the machine that produced a library's results. That
is the machine right up until the run is inside a container, where it is the container id.
The database already shows the problem:

     host      | claims |            newest
---------------+--------+-------------------------------
 ryzen-9950x   |    724 | 2026-08-21 05:16:09+00
 ryzen-5950x-2 |    220 | 2026-08-21 11:38:04+00
 e9725d308091  |     96 | 2026-08-21 11:53:48+00     <- wasm-jit, in a container
 ryzen-5950x-1 |     28 | 2026-08-21 11:17:19+00

e9725d308091 identifies no machine, and is gone with the container. Since #295 wants
every job running from a Docker image, that would become the answer everywhere and leave
the new libversion.host column as useless as having no column at all.

Jenkins knows the machine — it names its agents — and propagates NODE_NAME into a
container it starts, which is something socket.gethostname() inside that container
cannot see. So:

def hostname():
  explicit = os.environ.get("LIBTEST_HOST")
  if explicit:
    return explicit
  # Docker leaves /.dockerenv behind, podman /run/.containerenv.
  if os.path.exists("/.dockerenv") or os.path.exists("/run/.containerenv"):
    return os.environ.get("NODE_NAME") or socket.gethostname()
  return socket.gethostname()

NODE_NAME is consulted only inside a container. Outside one the kernel's answer is
the right one and a NODE_NAME left over in the environment must not override it — which
is also what makes this a no-op for the machines running the testing today. LIBTEST_HOST
overrides both, for the same reason LIBTEST_DB exists, and is the escape hatch if some
job turns out not to have NODE_NAME.

It lives in resultsdb as one helper used by both callers, so the host in job_claim and
the host stored with the results cannot disagree about which machine this is. That also
fixes the wasm-jit claims above, not just the new columns.

Checked all four paths — plain host; NODE_NAME set but no container (unchanged, the real
hostname wins); LIBTEST_HOST set; and inside a container with and without NODE_NAME.
The container paths were exercised by faking the marker file rather than in a real
container, since Docker was not available where this was written; worth a real check on a
node before #295 leans on it.

Part of #301, and needed before #295's Docker task means anything for attribution.

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generated by Claude Code