Add python-libguestfs to RPM list

libguestfs appears to be the best way to access images for injection,
so add the python bindings to the RPM list.  Indeed, on RHEL it is the
only way, because the fallback of nbd access isn't available.  There,
this change prevents a lot of errors in nova.virt.disk.vfs.localfs
when it can't import the nbd module.

Change-Id: I9c2a81bb7c26bc17f8b5f1b5a682c05a419b33ba
diff --git a/files/rpms/n-cpu b/files/rpms/n-cpu
index 149672a..e4fdaf4 100644
--- a/files/rpms/n-cpu
+++ b/files/rpms/n-cpu
@@ -4,3 +4,4 @@
 genisoimage
 sysfsutils
 sg3_utils
+python-libguestfs