Fix elasticsearch mapping path and content.

* modules/logstash/manifests/elasticsearch.pp: The file name for the
default elasticsearch mapping is default-mapping.json not
default_mapping.json. Fix this path.

* modules/logstash/files/elasticsearch.mapping.json: Add a missing
comma.

Change-Id: I36bbe6e125157b97f3333f383a8949b2a6b3ef5c
Reviewed-on: https://review.openstack.org/28484
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins