When hotplug hvm vcpu by 'xm vcpu-set' command, if it add/remove many vcpus by 1 'xm vcpu-set' command, it has a bug that it cannot add/remove all vcpus that want to be added/removed. This patch is to fix the bug. It delays trigger sci until all xenstore cpu node status are watched. Signed-off-by: Liu, Jinsong