XD-1: Inial commit of the HdfsItemWriter

A couple notes on this PR:

1. It is modeled after most of the other ItemWriter implementations in batch that work with non-transactional stores (files, Mongo, etc) in that the actual persistence is delayed until the last moment before committing.
2. I didn't see an obvious division between unit tests and integration tests in this project, so my test is actually both.  It is a unit test for the writer and it also executes the writer within the context of a job.  I'd like to factor that test out, I just need to understand where it belongs.