Major Description
AddBlock returns an error code related to whether writing the block to the WAL was successful or not. In cases where a WAL may be unavailable temporarily, the write would fail but it seems like we are not using the return code (see here).
For example, when using the Flume Receiver, we should be sending a n'ack back to Flume if the block wasn't written to the WAL. I haven't gone through the full code path yet but at least from looking at the ReceiverSupervisorImpl, it doesn't seem like that return code is being used.
