upgrades.md explains how to do upgrade from v1.4.3 to v1.4.6 as an
example. The versions are a little old, and the doc readers would
have a concern the upgrade works fine or not.
This updates versions after verifying the way works fine by hands.

kubeadm never rotates sa.key/sa.pub, so there is no need to delete tokens/restart pods

Signed-off-by: Etienne Champetier <e.champetier@ateme.com>

* Add prompt to upgrade node or delay before upgrade

* add docs

UPdate docs to match actuall required settings to perform an unsafe upgrade using cluster.yml playbook. Relates to https://github.com/kubernetes-sigs/kubespray/issues/4736 and https://github.com/kubernetes-sigs/kubespray/issues/4139 (#5609)

Since it is unsupported to skip upgrades, I've detailed the steps for upgrading a step at a time and removed some language that indicated it should work

* Add tags for cert serial tasks

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

* fixup kubernetes node

* Enable upgrade to kubeadm

* fix kubedns upgrade

* try upgrade route

* use init/upgrade strategy for kubeadm and ignore kubedns svc

* Use bin_dir for kubeadm

* delete more secrets

* fix waiting for terminating pods

* Manually enforce kube-proxy for kubeadm deploy

* remove proxy. update to kubeadm 1.8.0rc1

Clarify that the `kube_version` environment variable is needed for the CLI "graceful upgrade". Also add and example to check that the upgrade was successful.

- added -b and fixed typo in ansible-playbook command 
- fixed formatting issue

Based on #718 introduced by rsmitty.

Includes all roles and all options to support deployment of
new hosts in case they were added to inventory.

Main difference here is that master role is evaluated first
so that master components get upgraded first.

Fixes #694