Pass arg lists to gcloud as comma-separated single arg

This should get rid of the scary warning messages on GCE up.

Fixes #8117

cluster/gke/util.sh

@@ -167,7 +167,7 @@ function test-setup() {
   #                 collisions here?
   "${GCLOUD}" compute firewall-rules create \
     "${MINION_TAG}-${USER}-http-alt" \
-    --allow tcp:80 tcp:8080 \
+    --allow tcp:80,tcp:8080 \
     --project "${PROJECT}" \
     --target-tags "${MINION_TAG}" \
     --network="${NETWORK}"