* Fix not available config field in kubeadm-init.md
Update the line describing `unifiedControlPlaneImage`, since "unifiedControlPlaneImage" in ClusterConfiguration was changed to a boolean field called "useHyperKubeImage" in v1beta1.
( https://godoc.org/k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/v1beta1 )
* Update image names and versions in kubeadm-init.md
$ kubeadm config images list
k8s.gcr.io/kube-apiserver:v1.13.4
k8s.gcr.io/kube-controller-manager:v1.13.4
k8s.gcr.io/kube-scheduler:v1.13.4
k8s.gcr.io/kube-proxy:v1.13.4
k8s.gcr.io/pause:3.1
k8s.gcr.io/etcd:3.2.24
k8s.gcr.io/coredns:1.2.6
# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
k8s.gcr.io/kube-proxy v1.13.4 fadcc5d2b066 10 days ago 80.3MB
k8s.gcr.io/kube-controller-manager v1.13.4 40a817357014 10 days ago 146MB
k8s.gcr.io/kube-scheduler v1.13.4 dd862b749309 10 days ago 79.6MB
k8s.gcr.io/kube-apiserver v1.13.4 fc3801f0fc54 10 days ago 181MB
k8s.gcr.io/coredns 1.2.6 f59dcacceff4 4 months ago 40MB
k8s.gcr.io/etcd 3.2.24 3cab8e1b9802 5 months ago 220MB
k8s.gcr.io/pause 3.1 da86e6ba6ca1 14 months ago 742kB
* Update the way to use custom etcd image in kubeadm-init.md
According to rosti's [comment](https://github.com/kubernetes/kubeadm/issues/1255#issuecomment-439874004),
the `image` field under `etcd` (from `v1alpha3`) was replaced by a couple of fields - `imageRepository` and `imageTag`.
* Apply suggestions from @neolit123 in kubeadm-init.md
Suggestions from @neolit123: https://github.com/kubernetes/website/pull/13068#pullrequestreview-212806230
* Apply a suggestion from @rosti in kubeadm-init.md
A suggestion from @rosti : https://github.com/kubernetes/website/pull/13068#discussion_r264228348
Jihoon Seo
01ed12e4e3