The job open api starts a task and ties that AutodetectCommunicator.
The job close api is a sugar api, that uses the list and cancel task api to close a AutodetectCommunicator instance.
The flush job and post data api redirect to the node holding the job task and then delegate the flush or data to the AutodetectCommunicator instance.
Also:
* Added basic multi node cluster test.
* Fixed cluster state diffs bugs, forgot to mark ml metadata diffs as named writeable.
* Moved waiting for open job logic into OpenJobAction.TransportAction and moved the logic that was original there to a new action named InternalOpenJobAction.
Original commit: elastic/x-pack-elasticsearch@194a058dd2
