Bug 27043: Add to number_of_replicas and number_of_shards to index config

Bug 27043: Add to number_of_replicas and number_of_shards to index config

With Elasticsearch 6 (>6.4), we have a warning on index creation :
  the default number of shards will change from [5] to [1] in 7.0.0

See https://github.com/elastic/elasticsearch/pull/30587

I propose to add number_of_shards in index config.

Also add number_of_replicas that is better explicit.
In case on only one node, it must be 0.

Test plan :
1) Use Elasticsearch
2) Apply patch and flush memcached
3) Rebuild indexes : misc/search_tools/rebuild_elasticsearch.pl -v -b -d
4) Check you dont have a warning about number of shards
5) Check the settings of index :
   curl '<cluster>:9200/<myindex>_biblios/_settings?pretty&filter_path=**.number_of_*'
6) You should see :
   "number_of_shards" : "5",
   "number_of_replicas" : "1"

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>