The QEMU guest agent "/usr/bin/qemu-ga" has some handy functions
for controlling the guest, not least, shutdown/reboot and filesystem
freeze/thaw.
In Fedora 15/16 the semantics of the ACPI power button have been
changed to suspend-to-RAM which breaks our current shutdown
implementation.
By adding support for the agent we gain a more predictable way
to shutdown / reboot guests.
NB: the code currently has the same "flaw" as the monitor, in
so much as we wait forever for a guest agent reply. We need to
add a timeout ability to the agent code