[libvirt] [PATCH]: Fix sexpr generation again

DanB pointed out that my sexpr xend_internal patch from yesterday broke one of the regression tests. The problem is that the xenDaemonFormatSxpr{Disk,Net} functions are shared between domain creation time and attaching disk time. Unfortunately, though, Xend expects something different during these two times. During domain creation time, it wants the "(device" in front of the sexpr, while during attach time it does not. To remedy this situation, I added a flag to these two functions to differentiate between these two modes. With this patch in place, all of the regression tests pass. Signed-off-by: Chris Lalancette <clalance(a)redhat.com&gt;