Fix irrelevant-files in nova-dsvm-multinode-base

The nova-live-migration test hook configuration is in
nova/tests/live_migration/hooks and because of the
irrelevant-files list on the job, changes to those
setup scripts are not self-testing. This change fixes
the regex so we can self-test the nova-live-migration
job changes.

Change-Id: Ia7e35d483f660e98eea5e109e010f77d5419af85

.zuul.yaml

@@ -46,7 +46,7 @@
       - ^doc/.*$
       - ^nova/hacking/.*$
       - ^nova/locale/.*$
-      - ^nova/tests/.*$
+      - ^nova/tests/(?!live_migration).*$
       - ^releasenotes/.*$
       - ^setup.cfg$
       - ^tests-py3.txt$