Cluster healing

Cluster nodes can become unresponsive or unusable due to lost connectivity, daemons crashing, hardware issues and many other reasons. When this happens the COE will mark them as unusable or 'not ready' and reschedule workloads elsewhere, leaving the cluster at reduced capacity.

Magnum could handle the cluster recovery (healing) triggering node replacement or recovery whenever an issue is found. This could be done in two ways:
* triggered by the user, via a openstack coe cluster heal <cluster-id> command
* triggered by a periodic task, monitoring the state of the clusters