qemu: Honor 'restart' action for 'on_poweroff'

qemu: Honor 'restart' action for 'on_poweroff'

We simply terminate qemu instead of issuing a reset as the semantics of
the setting dictate.

Fix it by handling it identically to 'fake reboot'.

We need to forbid the combination of 'onReboot' -> 'destroy' and
'onPoweroff' -> reboot though as the handling would be hairy and it
honetly makes no sense.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>