dh_missing: ignore warning on libtool .la file

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>

debian/not-installed

+# libtool files for the shared libraries, not needed by end user
+usr/lib/*/*libvirt*.la
+usr/lib/libvirt/storage-file/libvirt_storage*.la
+usr/lib/libvirt/storage-backend/libvirt_storage_backend*.la
+usr/lib/libvirt/lock-driver/*.la
+usr/lib/libvirt/connection-driver/*.la