Fixes LOGSTASH-1328
Make ES index requests synchronous. Prior to this, I had incorrectly
assumed that elasticsearch acting as a client had a fixed-size thread
pool to limit the number of active bulk index requests. This now
executes bulk index requests one at a time.
Merge pull request #678 from jippi/patch-1

Fixes LOGSTASH-1328
Merge pull request #688 from logstash/synchronous-elasticsearch

Make ES index requests synchronous. Prior to this, I had incorrectly
Merge git://github.com/logstash/logstash