Kokoro: add delay between service and cluster deletions (#138)

* Kokoro: add delay between service and cluster deletions

* Address ahmetb's comments

.kokoro/e2e_tests_docker.sh

@@ -35,6 +35,9 @@ function cleanup {
   kubectl delete -f bookshelf-worker-${DATA_BACKEND}.yaml || true
   kubectl delete -f bookshelf-service.yaml || true
 
+  # Wait for service deletion to finalize
+  sleep 120;
+
   # Delete the cluster
   gcloud container clusters delete bookshelf --zone $ZONE -q || true
 
@@ -116,4 +119,4 @@ npm run e2e
 # Exit on error
 if [[ $CODE -ne 0 ]]; then
   exit $CODE
-fi
+fi