[libvirt] suspend/hibernate guests on host shutdown

There are times when you just have to reboot the host machine to clear a problem or after some maintenance. The problem right now is that this forces all the guests to go through an entire reboot as well. What would be good is if the host shutdown would invoke a suspend/hibernate of the guests and then restore the guests to their same condition on the reboot. The guests should notice nothing other that a small loss of wallclock time. Regards, Gerry