Allow creation of clusters larger than 500 nodes in GCE, take 2.

The change from the take 1 is to remove the suffix from the name of the
last MIG.

cluster/gce/upgrade.sh

@@ -174,6 +174,7 @@ function upgrade-nodes() {
 #
 # Vars set:
 #   SANITIZED_VERSION
+#   INSTANCE_GROUPS
 #   KUBELET_TOKEN
 #   KUBE_PROXY_TOKEN
 #   CA_CERT_BASE64
@@ -184,7 +185,7 @@ function prepare-node-upgrade() {
   echo "== Preparing node upgrade (to ${KUBE_VERSION}). ==" >&2
   SANITIZED_VERSION=$(echo ${KUBE_VERSION} | sed 's/[\.\+]/-/g')
 
-  detect-node-names
+  detect-node-names # sets INSTANCE_GROUPS
 
   # TODO(zmerlynn): Refactor setting scope flags.
   local scope_flags=
@@ -231,16 +232,18 @@ function do-node-upgrade() {
     subgroup="alpha compute"
   fi
   local template_name=$(get-template-name-from-version ${SANITIZED_VERSION})
-  gcloud ${subgroup} rolling-updates \
-      --project="${PROJECT}" \
-      --zone="${ZONE}" \
-      start \
-      --group="${NODE_INSTANCE_PREFIX}-group" \
-      --template="${template_name}" \
-      --instance-startup-timeout=300s \
-      --max-num-concurrent-instances=1 \
-      --max-num-failed-instances=0 \
-      --min-instance-update-time=0s
+  for group in ${INSTANCE_GROUPS[@]}; do
+    gcloud ${subgroup} rolling-updates \
+        --project="${PROJECT}" \
+        --zone="${ZONE}" \
+        start \
+        --group="${group}" \
+        --template="${template_name}" \
+        --instance-startup-timeout=300s \
+        --max-num-concurrent-instances=1 \
+        --max-num-failed-instances=0 \
+        --min-instance-update-time=0s
+  done
 
   # TODO(zmerlynn): Wait for the rolling-update to finish.