use master branch for mk labs

Change-Id: Ifb67474a3fbf9d689f7f7a7f17c8fb3cdaab042f
diff --git a/jenkins/client/job/deploy/lab/mk/init.yml b/jenkins/client/job/deploy/lab/mk/init.yml
index 6f95e30..0bcfbc0 100644
--- a/jenkins/client/job/deploy/lab/mk/init.yml
+++ b/jenkins/client/job/deploy/lab/mk/init.yml
@@ -40,7 +40,7 @@
                 default: "gerrit"
               HEAT_TEMPLATE_BRANCH:
                 type: string
-                default: "composite"
+                default: "master"
               HEAT_STACK_NAME:
                 type: string
                 description: Heat stack name. Will be generated if missing.