A large number of `[2019-03-22T14:19:52,864][WARN ][org.elasticsearch.deprecation.common.ParseField] Deprecated field [_retry_on_conflict] used, expected [retry_on_conflict] instead` messages are seen on the upgraded elasticsearch 6 nodes.
* [T215615] Setting a negative [weight] in Function Score Query is deprecated and will throw an error in the next major version
* _retry_on_conflict -> retry_on_conflict
* [nested_path] has been deprecated in favour of the [nested] parameter
* [nested_filter] has been deprecated in favour of the [nested] parameter
* Deprecated field [auto_generate_phrase_queries] used, replaced by [This setting is ignored, use [type=phrase] instead to make phrase queries out of all text that is within query operators, or use explicitly quoted strings if you need finer-grained control]