Update Elasticsearch Output Plugin to retry bulk

Some actions may fail within the ES client bulk call.
Now, some messages (specifically errors 429 and 503s) will be
retried up to 3 times. If there are still actions that are
unsuccessfully indexed, Stud Buffer will continue its current
behavior (to retry indefinitely).

Stud Buffer will replay all events it first attempted to flush
to Elasticsearch. This means duplicate events may find themselves
in Elasticsearch.

(migrated from https://github.com/elasticsearch/logstash/pull/1997 with a few modifications to make 
tests run once plugin is installed)
Yes. It requires extra level parsing of the item to check what type it is (createIndex, update, etc) and getting that. I can go ahead and add the extra logic. figured this gets the job done without extra parsing. The only status codes are either Created(201) or Ok(200).