@Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
          promise.tryFailure(cause);
        }
Helper class for implementing {@link FanOutOneBlockAsyncDFSOutput}.
hbase-asyncfs/src/main/java/org/apache/hadoop/hbase/io/asyncfs/FanOutOneBlockAsyncDFSOutputHelper.java