Stats can be retrieved on a per-feature / per-component basis including the fields
they apply to. This commit add support for a 'completion' flag to include statistics
for the complition feature as well as 'completion_fields' to only
include certain fields into the returned statistics.
To disambiguate between 'fielddata' and 'completion' fields this commit
uses 'fields' as the default inclusion filter for stats fields only used
if not dedicated '[completion|fielddata]_fields' paramter is provided.
Relates to #3522
Refresh flag in optimize is problematic, since the shards refresh is allowed to execute on is different compared to the optimize shards. In order to do optimize and then refresh, they should be executed as separate APIs when needed.
closes#3690
Refresh flag in flush is problematic, since the shards refresh is allowed to execute on is different compared to the flush shards. In order to do flush and then refresh, they should be executed as separate APIs when needed.
closes#3689
/_template shows: No handler found for uri [/_template] and method [GET]
It would make sense to list the templates as they are listed in the /_cluster/state call.
Closes#2532.