anchor.diff:  All settings under the `discovery.zen` namespace, which existed only for BWC reasons in 7.x,
   are no longer supported. In particular, this includes:
   
  +- `discovery.zen.minimum_master_nodes`
   - `discovery.zen.no_master_block`
   - `discovery.zen.hosts_provider`
   - `discovery.zen.publish_timeout`
  
positive.code: *Impact* +
  Discontinue use of the `discovery.zen` settings. Specifying these settings in
  `elasticsearch.yml` will result in an error on startup.
  ====
negative.code: - `discovery.zen.fd.register_connection_listener`
  - `discovery.zen.join_retry_attempts`
  - `discovery.zen.join_retry_delay`
  - `discovery.zen.join_timeout`
  - `discovery.zen.max_pings_from_another_master`
  - `discovery.zen.send_leave_request`
  - `discovery.zen.master_election.wait_for_joins_timeout`
  