Comment 17 for bug 1014647

Cirros is able to do soft reboot.

If you decrease the build timeout below the soft reboot timeout (120 sec) the basic minimum scenario will fail if nova falls back to the hard reboot.

The other way is, you can modify the acpid action to power button, which is more visible than just reboot.
But in this case you assume, the image using the acpid for handling the event (different image may have different way), and you may also expect something about how the acpid configuration files are organized.