domain_shutdown() needs to call raise_softirq(SCHEDULE_SOFTIRQ).
This forces the current vcpu to be rescheduled and paused.
Without this, during live migrate, if another vcpu has defer_shutdown==1
then the current vcpu can return from domain_shutdown(),
do a vmenter, and continue running guest code, "resume" code that
should only be running on the receiving node!

Signed-off-by: Robert Phillips <rphillips@virtualiron.com>
Signed-off-by: Ben Guthro <bguthro@virtualiron.com>