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.
Any thoughts on options for specifying ssl certificates or CAs (for server verification) and specifying ssl client key+cert for the server to authenticate our connection?