Glusterfs: use automatic mtime-based split-brain resolution

Change-Id: I9975d30dd57721a8703d4144ba3d6c1909a789c1
diff --git a/glusterfs/server/volume/keystone.yml b/glusterfs/server/volume/keystone.yml
index 2515fca..81e14be 100644
--- a/glusterfs/server/volume/keystone.yml
+++ b/glusterfs/server/volume/keystone.yml
@@ -15,6 +15,7 @@
             network.remote-dio: On
             diagnostics.client-log-level: WARNING
             diagnostics.brick-log-level: WARNING
+            cluster.favorite-child-policy: mtime
         keystone-credential-keys:
           storage: /srv/glusterfs/keystone-credential-keys
           replica: 3
@@ -28,3 +29,4 @@
             network.remote-dio: On
             diagnostics.client-log-level: WARNING
             diagnostics.brick-log-level: WARNING
+            cluster.favorite-child-policy: mtime