- force body to a string (was an array, join with "") to make FTW send a fixed-size request (avoid chunking).
- force body to a string (was an array, join with "") to make FTW send a
fixed-size request (avoid chunking).

The idea here is to avoid the previous behavior that logstash sends 2
chunks per event to index (once for bulk header, once for document).
Many small chunks isn't very efficient, and until we make a more
efficient chunk sender, this will suffice.

joekiller/logstash-kafka,opentable/logstash-kafka,joekiller/logstash-kafka,Aloomaio/logstash-kafka,tinglinux/logstash-kafka,opentable/logstash-kafka,Aloomaio/logstash-kafka,tinglinux/logstash-kafka