Add a default_mapping to elasticsearch.

* Don't store or index `_all`.
* Compress `_source` (which is stored but not indexed by default).
* Create a dynamic template for the string type.
* Only analyze the index of `@message` strings.

This is a very rudimentary config, and should probably be expanded
on by someone who has a deeper understanding of elasticsearch.

Change-Id: I14052c48c7bb6f05e259615a5203dc1ad87a08af
Reviewed-on: https://review.openstack.org/28216
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Jesse Keating <jesse.keating@rackspace.com>
Approved: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins