[elasticsearch] Add migration for Kibana 6.x index

Elasticsearch 6.x dropped support for mapping types[1], which by default
the Kibana index used. This means that when deploying ELK 6.x, the
Kibana index must be migrated to the new schema to preserve dashboards
and visualizations. There is a process defined[2], which involves
creating a new index with the specified schema, then reindexing the old
index's data into the new index, then doing a rename/delete.

This adds support for that workflow via Ansible. It takes place after
the ES container is restarted after an upgrade, so there will be a
(short) period of time where the Kibana index is not migrated. During
this time, Kibana still loads, but presents the user with a status
screen informing that the index needs migration.

[1]:
https://www.elastic.co/guide/en/elasticsearch/reference/6.x/removal-of-types.html
[2]: https://www.elastic.co/guide/en/kibana/6.x/migrating-6.0-index.html

Implements: blueprint elasticsearch-kibana-version-upgrade
Depends-On: https://review.opendev.org/709624
Change-Id: I4550629e2113f3da7f1cecfeab0d5fe0d899dae8