change shell var MINION_SCOPES to user setable

Because bash arrays may not be environment variables
 (see: <https://stackoverflow.com/questions/5564418/exporting-an-array-in-bash-script>)
 we have to change the MINION_SCOPES array to a string
* prefers aliases instead of full URLs for scopes

tested under GKE, needs GCE testing

Close #10458

cluster/gke/util.sh

@@ -112,6 +112,7 @@ function verify-prereqs() {
 #   ZONE
 #   CLUSTER_API_VERSION (optional)
 #   NUM_MINIONS
+#   MINION_SCOPES
 function kube-up() {
   echo "... in kube-up()" >&2
   detect-project >&2
@@ -142,6 +143,7 @@ function kube-up() {
     "--project=${PROJECT}"
     "--num-nodes=${NUM_MINIONS}"
     "--network=${NETWORK}"
+    "--scopes=${MINION_SCOPES}"
   )
   if [[ ! -z "${DOGFOOD_GCLOUD:-}" ]]; then
     create_args+=("--cluster-version=${CLUSTER_API_VERSION:-}")