Fix build on Ubuntu.

Fix build on Ubuntu.

When building on Ubuntu with make -j3 (or more), it would always
fail when trying to build virt-aa-helper.  I'm not an expert in
automake by any means, but I think the entry for virt-aa-helper
is mis-using LDADD; it shouldn't be putting direct paths to
libvirt_conf.la and libvirt_util.la, but instead referencing those
names.  With this patch in place, I'm able to successfully build
on Ubuntu 9.04 with make -j3.

Signed-off-by: Chris Lalancette <clalance@redhat.com>