Run GKE tests on stable cluster

Author: szh

deploy/summon/secrets.yml

@@ -20,7 +20,7 @@ common:
   IMAGE_PULL_SECRET: dockerpullsecret
 
 gke:
-  GCLOUD_CLUSTER_NAME: !var ci/gke/rapid/cluster-name
+  GCLOUD_CLUSTER_NAME: !var ci/gke/stable/cluster-name
   GCLOUD_ZONE: !var ci/gke/zone
   GCLOUD_PROJECT_NAME: !var ci/gke/project-name
   GCLOUD_SERVICE_KEY: !var:file ci/gke/service-key