This commit adds the max_running_jobs setting from elasticsearch.yml
into a node attribute called ml.max_open_jobs. Previously there was
an assumption that max_running_jobs would be the same for all nodes in
the cluster. However, during a rolling cluster restart where the value
of the setting is being changed this clearly cannot be the case, and
would cause unexpected/unpredictable limits to be used during the period
when different nodes had different settings.
For backwards compatibility, if another node in the cluster has not added
its setting for max_running_jobs to the cluster state then the old
(flawed but better than nothing) approach is applied, i.e. assume the
remote node's setting for max_running_jobs is equal to that of the node
deciding the job allocation.
Relates elastic/x-pack-elasticsearch#2185
Original commit: elastic/x-pack-elasticsearch@1e62b89183
22da5cf89e