coreos-base/oem-gce: bring back shutdown scripts

[tormath1]

In the init.sh of the OEM GCE container, we have the following
section:

wait -n "${daemon_pids[@]}" || :
kill "${daemon_pids[@]}" || :

test -n "$stopping" || exit 1

exec /usr/bin/google_metadata_script_runner --script-type shutdown

shutdown script was not executed because container was receiving a
SIGKILL, the started processes was not properly terminated.

According to the systemd-nspawn manual:

If --boot is not used and this option is not specified
the container's processes are terminated abruptly via SIGKILL

Signed-off-by: Mathieu Tortuyaux mtortuyaux@microsoft.com

---

Testing done

Added a shutdown-script to the GCP metadata server, edited the oem-gce to add the --kill-signal=SIGTERM, manually stopped the service and see the shutdown-script being executed in the logs:

Trying to halt container. Send SIGTERM again to trigger immediate termination.
++ stopping=1
++ kill 30 31 32
+ :
+ kill 30 31 32
+ test -n 1
+ exec /usr/bin/google_metadata_script_runner --script-type shutdown
Stopping GCE Linux Agent...
INFO Starting shutdown scripts.
INFO Found shutdown-script in metadata.
INFO shutdown-script: Return code 0.
INFO Finished running shutdown scripts.
Container oem-gce exited successfully.
oem-gce.service: Deactivated successfully.
Stopped GCE Linux Agent.
oem-gce.service: Consumed 4.964s CPU time.

• Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update)

Closes: flatcar/Flatcar#743

[tormath1]

cherry-picked to:

• flatcar-3227
• flatcar-3139
• flatcar-3248