Bump 4.5 to elasticsearch 2.3

[epixa]

Kibana 4.5 must be updated to require elasticsearch 2.3. At a minimum, this means updating the esvm config and the elasticsearch plugin config, though there may be other places (readme?).

[epixa]

The version requirement check was updated in the PR. Now we just need to make sure the elasticsearch version in the esvm config gets updated whenever 2.3 exists.

[jbudz]

Closed by #6594