As noted in the review of CDRIVER-3230, our logic for batching write operations for OP_QUERY seems a little off. We fit in as many documents as we can into maxBsonObjectSize + 16K allowance, but really, our logic should be:

1. Add bulk write documents to current batch until we reach maxBsonObjectSize
2. Add our command metadata (check that the metadata itself does not exceed 16K allowance)
3. Send, and start new batch