Added optional username and password to elasticsearch_http output plugin. Fixes LOGSTASH-902.
Merge branch 'master' into logstash-902
Merge branch 'master' of https://github.com/logstash/logstash into logstash-902
Set the password config option to validate as a password.
Merge pull request #684 from ianneub/logstash-902

Fix for LOGSTASH-902 - Added optional username and password to elasticsearch_http output plugin