send/receive: use io.ReadCloser and io.WriteCloser instead of io.Reader / io.Writer

[casKd-dev]

Current implementation of send/receive hangs until exit due to the stream never being closed, thus blocking indefinetly. For these functions the data types implementing io.Close() should be used and stream closures propagated accordingly.

Unsure about the file descriptor provided by the raw ioctl() call but go's cmd.Exec / cmd.Run requires directly using the o.StdoutPipe() so that Close() is propagated accordingly.