Try to hard-reboot on rerun of post even on emulators.

Try to hard-reboot on rerun of post even on emulators.

Extend the hard-reboot logic to qemu and kvm.  On qemu, a reboot will
not reset the memory settings for 0xc0000-0xfffff, so copy that memory
area manually before rebooting.  Unfortunately, kvm does not keep a
pristine copy of the BIOS at 0xffff0000, so detect that case and
shutdown the machine.