Add extra_formulas for cookiecutter testing

Change-Id: Iaafbe3783486460946975b370cad9eeca8fefde6
diff --git a/jenkins/client/job/salt-models/tests.yml b/jenkins/client/job/salt-models/tests.yml
index 9ce9c31..c2c8996 100644
--- a/jenkins/client/job/salt-models/tests.yml
+++ b/jenkins/client/job/salt-models/tests.yml
@@ -130,3 +130,6 @@
               PARALLEL_NODE_GROUP_SIZE:
                 type: string
                 default: "1"
+              EXTRA_FORMULAS:
+                type: string
+                default: "xtrabackup"