Add SSL and authentication support for the HTTP protocol of output elasticsearch

Should fix https://github.com/elasticsearch/logstash/issues/1453.

Due to the Faraday dependency, it seems on some version of Ruby, Faraday, OpenSSL and/or your HTTPS backend, the request will fail, even though the response stream seems OK.
Yes we could definitely use the client cert authentication. For us it is easier to just deploy to our instances with just an hardcoded Basic auth, but yes it would be doable.