This commit fixes ping timeout settings inconsistencies in
ZenDiscovery. In particular, the documentation refers to the ping
timeout setting as discovery.zen.ping_timeout but the code was
ultimately using discovery.zen.ping.timeout if this was set.
This commit also changes all instances of the raw string
“discovery.zen.ping_timeout” to the constant
o.e.d.z.ZenDiscovery.SETTING_PING_TIMEOUT.
Finally, this commit removes the legacy setting
"discovery.zen.initial_ping_timeout".
Closes#6579, #9581, #9908
* Dropped ScoreType in favour of Lucene's ScoreMode
* Removed `score_type` option from `has_child` and `has_parent` queries in favour for the already existing `score_mode` option.
* Removed the score mode `sum` in favour for the already existing `total` score mode. (`sum` doesn't exist in Lucene's ScoreMode class)
* If `max_children` is set to `0` it now really means that zero children are allowed to match.