This pull request removes the relationship between the state
of persistent task (as stored in the cluster state) and the status
of the task (as reported by the Task APIs and used in various
places) that have been confusing for some time (#29608).
In order to do that, a new PersistentTaskState interface is added.
This interface represents the persisted state of a persistent task.
The methods used to update the state of persistent tasks are
renamed: updatePersistentStatus() becomes updatePersistentTaskState()
and now takes a PersistentTaskState as a parameter. The
Task.Status type as been changed to PersistentTaskState in all
places were it make sense (in persistent task customs in cluster
state and all other methods that deal with the state of an allocated
persistent task).
992c7889ee