ElasticSearch Plugin should support SSL configuration

## Feature Request

The ElasticSearch plugin currently doesn't support SSL as the HTTP JSON endpoint does.
### Proposal:

Make the ES plugin work with SSL.
### Current behavior:

The ES plugin fails when connecting to an SSL enabled ES node.
### Desired behavior:

The ES plugin doesn't fail.
### Use case:

All of our ES nodes run with SSL enabled. So not having this makes the ES plugin not usable.
