Set number of faceting indexes to 1 in Kibana.

* modules/kibana/files/config.rb: Kibana uses ElasticSearch's faceting
feature to collect statistics. It defaults to performing this over all
indexes but this is expensive so limit it to 1 index.

Change-Id: I324099f88a9855062aba4905380c9dc8540555a5
Reviewed-on: https://review.openstack.org/28202
Reviewed-by: K Jonathan Harker <jesusaurus@mail.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins