set HEAT_STACK_NAME if not defined

Change-Id: I7087c3a49a84b11a758c28531d1d7bdfb52ee6e8
diff --git a/mk-k8s-simple-deploy-pipeline.groovy b/mk-k8s-simple-deploy-pipeline.groovy
index 267512d..84897cb 100644
--- a/mk-k8s-simple-deploy-pipeline.groovy
+++ b/mk-k8s-simple-deploy-pipeline.groovy
@@ -33,6 +33,10 @@
     def openstackVersion = OPENSTACK_API_CLIENT ? OPENSTACK_API_CLIENT : "liberty"
     def openstackEnv = "${env.WORKSPACE}/venv"
 
+    if (HEAT_STACK_NAME == "") {
+	HEAT_STACK_NAME = "mk-k8s-simple-b" + BUILD_NUMBER
+    }
+
     stage ('Download Heat templates') {
         git.checkoutGitRepository('template', HEAT_TEMPLATE_URL, HEAT_TEMPLATE_BRANCH, HEAT_TEMPLATE_CREDENTIALS)
     }