Add build-user-vars plugin to app release build

Change-Id: I61ddfe474904d000d3444d3a01df0faa87ea6b4e
diff --git a/jjb/onos-app-release.yaml b/jjb/onos-app-release.yaml
index 25a2f8b..5790821 100644
--- a/jjb/onos-app-release.yaml
+++ b/jjb/onos-app-release.yaml
@@ -26,6 +26,7 @@
       - ssh-agent-credentials:
           users:
               - 'gerrit-jenkins-user'
+      - build-user-vars
 
     parameters:
       - string: