Remove duplicate code for NettyHBaseSaslRpcServerHandler and make the sentByte metrics more accurate

private void doResponse(ChannelHandlerContext ctx, SaslStatus status, Writable rv,
    String errorClass, String error) throws IOException {
    // In my testing, have noticed that sasl messages are usually
    // in the ballpark of 100-200. That's why the initial capacity is 256.
    ByteBuf resp = ctx.alloc().buffer(256);
    try (ByteBufOutputStream out = new ByteBufOutputStream(resp)) {
      out.writeInt(status.state); // write status
      if (status == SaslStatus.SUCCESS) {
        rv.write(out);
      } else {
        WritableUtils.writeString(out, errorClass);
        WritableUtils.writeString(out, error);
      }
    }
    NettyFutureUtils.safeWriteAndFlush(ctx, resp);
  }

protected final void doRawSaslReply(SaslStatus status, Writable rv, String errorClass,
    String error) throws IOException {
    BufferChain bc;
    // In my testing, have noticed that sasl messages are usually
    // in the ballpark of 100-200. That's why the initial capacity is 256.
    try (ByteBufferOutputStream saslResponse = new ByteBufferOutputStream(256);
      DataOutputStream out = new DataOutputStream(saslResponse)) {
      out.writeInt(status.state); // write status
      if (status == SaslStatus.SUCCESS) {
        rv.write(out);
      } else {
        WritableUtils.writeString(out, errorClass);
        WritableUtils.writeString(out, error);
      }
      bc = new BufferChain(saslResponse.getByteBuffer());
    }
    doRespond(() -> bc);
  }