Hostname must be a valid DNS name, which is checked as https://github.com/kubernetes/apimachinery/blob/master/pkg/util/validation/validation.go#L115

The situation I have encountered is that my hostname contained underscore which is disallowed and apiserver refused to start.

Fix DiscoveryTokenCACertHashes key to discoveryTokenCACertHashes in kubeadm-client.conf

Upgrade Kubernetes to V1.11.2
The kubeadm configuration file version has been upgraded from v1alpha1 to v1alpha2
Add bootstrap kubeadm-config.yaml with external etcd

Use helm install or support in future

Even without this PR, the operation works well.
However, it is better to use a single slash rather than
a double slash in the path.

This fixes #3014

apiserver cert should be created only once

ingress-nginx 0.16.2 (https://github.com/kubernetes/ingress-nginx/releases/tag/nginx-0.16.2)

This patch simplify ingress-nginx deployment by default deploy on
master, with customizable options; on the other hand, remove the
additional Ansible group "kube-ingress" and its k8s node label
injection.

Reference to https://kubernetes.io/docs/concepts/services-networking/ingress/#prerequisites:

    GCE/Google Kubernetes Engine deploys an ingress controller on the master.

By changing `ingress_nginx_nodeselector` plus custom k8s node
label, user could customize the DaemonSet deployment target.

If `ingress_nginx_nodeselector` is empty, will deploy DaemonSet on
every k8s node.

The referenced issue (https://github.com/kubernetes/kubeadm/issues/441) has already been fixed.

* Add tags for cert serial tasks

This will help facilitate tag-based deployment of specific components.

* fixup kubernetes node

On Aarch64, the default cgroup driver for docker is systemd
instead of cgroupfs. Should conform kubelet to use systemd
as cgroup driver as well to keep it consistent with docker.

Without this change, below exception will be raised.
/usr/bin/docker-current: Error response from daemon: shim
error: docker-runc not installed on system.

Change-Id: Id496ec9eaac6580e4da2f3ef1a386c9abc2a5129