lguest: Allow running under paravirt-enabled KVM.

We actually can run under KVM, as it doesn't paravirtualize anything we
need to use; reduce the check to checking we are the normal ringlevel.

Reported-by: Stefanos Geraggelos <sgerag@cslab.ece.ntua.gr>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au># HG changeset patch