Adding nova-live-migration job in devstack gate

nova-live-migration is legacy job and  and rely on
devstack-gate + devstack setting so any change in devstack can
break it. Example bug: 1860021

We can remove this job once it is migrated to zuulv3 native.

Change-Id: Ie34d4dc1ab30ced8161796fe32628db07de86cc9
Related-bug: #1860021

Author: Ghanshyam

.zuul.yaml

@@ -622,6 +622,15 @@
             irrelevant-files:
               - ^.*\.rst$
               - ^doc/.*$
+        # NOTE(gmann): Remove this job from devstack pipeline once it is
+        # migrated to zuulv3 native. This is legacy job and rely on
+        # devstack-gate + devstack setting so any change in devstack can
+        # break it.
+        - nova-live-migration:
+            voting: false
+            irrelevant-files:
+              - ^.*\.rst$
+              - ^doc/.*$
     gate:
       jobs:
         - devstack