Include bug-presubj

Many reports don't contain any valuable information. Hopefully this
improves things.

debian/bug-presubj

+When reporting issues regarding libvirt and libvirtd please make sure you at
+least include the relevant log parts and your vm configuration.
+
+http://wiki.debian.org/libvirt/Debugging has more information on howto provide
+debugging information for the virt-* tools.