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.
@jsvd we dropped this and went with logstash-forwarder instead, and a cluster of logstash using plain HTTP with no auth to contact ES on a secure network.