fix quotes

Change-Id: I2c9b018ee48a3db0c6c9d32e5001c50f4c99685f
diff --git a/mk-k8s-cleanup-pipeline.groovy b/mk-k8s-cleanup-pipeline.groovy
index b9ac9b1..2a59bf6 100644
--- a/mk-k8s-cleanup-pipeline.groovy
+++ b/mk-k8s-cleanup-pipeline.groovy
@@ -24,7 +24,7 @@
 
     // value defaults
     def openstackVersion = OPENSTACK_API_CLIENT ? OPENSTACK_API_CLIENT : 'liberty'
-    def openstackEnv = '${env.WORKSPACE}/venv'
+    def openstackEnv = "${env.WORKSPACE}/venv"
 
     stage('Install OpenStack env') {
         openstack.setupOpenstackVirtualenv(openstackEnv, openstackVersion)