Currently we hardcode these defaults for installing VMs:
<on_poweroff>destroy</on_poweroff>
<on_reboot>destroy</on_reboot>
<on_crash>destroy</on_crash>
And these for post-install config:
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
But this has some issues. on_crash=restart is problematic in that most
configs don't support it, and some like virtuozzo actively reject it.
Additionally this we should leave as much to libvirt defaults as we
can, which are more sensible in this case.
Drop everything except setting on_reboot=destroy for the install time
case (which is required for our config changes). Since on_poweroff
and on_crash already default to 'destroy', the install time config
is unchanged, and the post-install config now on_crash=destroy instead
of 'restart'.
The s390 on_crash=preserve workaround is dropped, which was intended
to avoid a reboot loop caused by on_crash=reboot
fc6778108b