Add backupninja to EXTRA_FORMULAS

Change-Id: I07722a56ffd7d10e9e8b0b00f30778b26ceb0943
diff --git a/jenkins/client/job/salt-models/tests.yml b/jenkins/client/job/salt-models/tests.yml
index 5e7e82b..0440b28 100644
--- a/jenkins/client/job/salt-models/tests.yml
+++ b/jenkins/client/job/salt-models/tests.yml
@@ -164,7 +164,7 @@
                 default: "1"
               EXTRA_FORMULAS:
                 type: string
-                default: "xtrabackup docker haproxy aptly keepalived gerrit jenkins openldap maas"
+                default: "xtrabackup docker haproxy aptly keepalived gerrit jenkins openldap maas backupninja"
       job:
         test-salt-model-node:
           name: test-salt-model-node