DFS Write pipeline does not detect defective datanode correctly if it times out.

When DFSClient is writing to DFS, it does not correctly detect the culprit datanode (rather datanodes do not inform) properly if the bad node times out. Say, the last datanode in in 3 node pipeline is is too slow or defective. In this case, pipeline removes the first two datanodes in first two attempts. The third attempt has only the 3rd datanode in the pipeline and it will fail too. If the pipeline detects the bad 3rd node when the first failure occurs, the write will succeed in the second attempt.

I will attach example logs of such cases. I think this should be fixed in 0.17.x.