Automatically download the latest stable release version of

Kubernetes. Echo error to stderr. Simplify expression for
KUBE_VERSION. Explicitly match beginning of string.

cluster/get-kube.sh

@@ -72,7 +72,7 @@ function get_latest_version_number {
   elif [[ $(which curl) ]]; then
     curl -Ss ${latest_url}
   else
-    echo "Couldn't find curl or wget.  Bailing out."
+    echo "Couldn't find curl or wget.  Bailing out." >&2
     exit 4
   fi
 }