Append an alpha label to the exclude load balancer annotation.

cmd/kubeadm/app/constants/constants.go

@@ -136,7 +136,7 @@ const (
 
 	// LabelNodeRoleExcludeBalancer specifies that the node should be
 	// exclude from load balancers created by a cloud provider.
-	LabelNodeRoleExcludeBalancer = "node-role.kubernetes.io/exclude-balancer"
+	LabelNodeRoleExcludeBalancer = "alpha.node-role.kubernetes.io/exclude-balancer"
 
 	// MasterConfigurationConfigMap specifies in what ConfigMap in the kube-system namespace the `kubeadm init` configuration should be stored
 	MasterConfigurationConfigMap = "kubeadm-config"