Bulk hinting

With the introduction of the BulkOutputFormat, there may be cases where someone would like to tolerate node failures and have the job complete, but afterwards since we streamed they have to repair or rely on read repair. We don't currently have any way of hinting streams, but a node could take a snapshot before acknowledging the stream session, then remember to send the files in the snapshot to the unavailable nodes when they come back up. This isn't quite ideal since of course the node may have compacted these files, however it's much simpler than any sort of key tracking at this scale.