should have some way to indicate shutdown or reboot

At [1], I put in place change like below as a way to shut down cleanly, and
avoid the annoying messages cloud-init spews if you run /sbin/poweroff from
inside a user-data script.

Basically, at the end of my user-data I would do something like this:
# delay the poweroff to avoid annoying cloud-init messages
sh -fc 'i=0; while [ $i -lt 30 ] && i=$(($i+1)); do
    state=$(status cloud-final);
    set -- $state
    case "$2" in
      stop/*) poweroff; exit 0;;
    esac
    echo "$state [$2] after $i"
    sleep 1
  done
  echo "giving up after 30 seconds"
  poweroff' </dev/null &

That actually works fine, but its a bit more involved than it should be.
I can think of 2 ways to somewhat cleanly expose this:
 cloud-init request-poweroff [type [delay]]
where 'type' would be 'reboot', 'poweroff' ...
and cloud-init would somehow handle making that happen "delay" seconds after
it finished cloud-final.

Secondly, it'd be nice to have that as a cloud-config option also.
  #cloud-config
  shutdown: reboot 30

request-poweroff could just put a marker file in /run that would be read when
cloud-final finished.

[1] https://code.launchpad.net/~smoser/maas/cleaner-shutdown/+merge/128807