fix instance_zone name

Change-Id: Id8e05d670de7876f51fc5546ec5b41bb0979cbce
diff --git a/mk-lab-pipeline.groovy b/mk-lab-pipeline.groovy
index 28d72b3..7a21e16 100644
--- a/mk-lab-pipeline.groovy
+++ b/mk-lab-pipeline.groovy
@@ -69,7 +69,7 @@
     if (HEAT_STACK_REUSE == 'false') {
         stage('Launch new Heat stack') {
             envParams = [
-                'availability_zone': HEAT_STACK_ZONE,
+                'instance_zone': HEAT_STACK_ZONE,
                 'public_net': HEAT_STACK_PUBLIC_NET
             ]
             openstack.createHeatStack(openstackCloud, HEAT_STACK_NAME, HEAT_STACK_TEMPLATE, envParams, HEAT_STACK_ENVIRONMENT, openstackEnv)