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.
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
Justin Downing
Vincent Schwarzer
Matthew Mosesohn