Robustly cleanup MIG template on GCE teardown

cluster/gce/util.sh

@@ -769,6 +769,11 @@ function kube-down {
   echo "Bringing down cluster"
   set +e  # Do not stop on error
 
+  # Get the name of the managed instance group template before we delete the
+  # managed instange group. (The name of the managed instnace group template may
+  # change during a cluster upgrade.)
+  local template=$(get-template "${PROJECT}" "${ZONE}" "${NODE_INSTANCE_PREFIX}-group")
+
   # The gcloud APIs don't return machine parseable error codes/retry information. Therefore the best we can
   # do is parse the output and special case particular responses we are interested in.
   if gcloud preview managed-instance-groups --project "${PROJECT}" --zone "${ZONE}" describe "${NODE_INSTANCE_PREFIX}-group" &>/dev/null; then
@@ -792,11 +797,11 @@ function kube-down {
     fi
   fi
 
-  if gcloud compute instance-templates describe --project "${PROJECT}" "${NODE_INSTANCE_PREFIX}-template" &>/dev/null; then
+  if gcloud compute instance-templates describe --project "${PROJECT}" "${template}" &>/dev/null; then
     gcloud compute instance-templates delete \
       --project "${PROJECT}" \
       --quiet \
-      "${NODE_INSTANCE_PREFIX}-template"
+      "${template}"
   fi
 
   # First delete the master (if it exists).
@@ -886,6 +891,22 @@ function kube-down {
   set -e
 }
 
+# Gets the instance template for the managed instance group with the provided
+# project, zone, and group name. It echos the template name so that the function
+# output can be used.
+#
+# $1: project
+# $2: zone
+# $3: managed instance group name
+function get-template {
+  # url is set to https://www.googleapis.com/compute/v1/projects/$1/global/instanceTemplates/<template>
+  local url=$(gcloud preview managed-instance-groups --project="${1}" --zone="${2}" describe "${3}" | grep instanceTemplate)
+  # template is set to <template> (the pattern strips off all but last slash)
+  local template="${url##*/}"
+  echo "${template}"
+}
+
+
 # Checks if there are any present resources related kubernetes cluster.
 #
 # Assumed vars:
@@ -894,7 +915,6 @@ function kube-down {
 #   ZONE
 # Vars set:
 #   KUBE_RESOURCE_FOUND
-
 function check-resources {
   detect-project