Send @metadata.beat to Logstash instead of @metadata.index to prevent possible name clashes and give user full control over index name used for Elasticsearch elastic/libbeat#231
Add logging messages for bulk publishing in case of error elastic/libbeat#229
Add option to configure number of parallel workers publishing to Elasticsearch or Logstash.
Set default bulk size for Elasticsearch output to 50.
Set default http timeout for Elasticsearch to 90s.
Improve publish retry if sync flag is set by retrying only up to max bulk size events instead of all events to be published.