Automatic merge from submit-queue
Prompt user to use secure config in kubeadm
If don't set the kubeconfig, the default action is to use insecure port to connect to apiserver. It's necessary to tell people to use the admin.kubeconfig
```
#kubectl cluster-info
Kubernetes master is running at http://localhost:8080
KubeDNS is running at http://localhost:8080/api/v1/proxy/namespaces/kube-system/services/kube-dns
To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
```