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.
Is this still an issue?
Since both FTW::Agent and Elasticsearch::Client are used in HTTPClient, adding only auth and crypto options to `@agent` and not `@client` will make `template_put` and `template_exists?` calls fail, right?