Thread runner for reading lines of from a subprocess into a buffer.

        :param name: The logical name of the stream (used for logging only).
        :param stream: The stream to read from. This will typically a pipe
                       connected to the output stream of a subprocess.
        :param outbuf: The list to append the read lines to.

def _reader(self, name, stream, outbuf):
        """
        Thread runner for reading lines of from a subprocess into a buffer.

        :param name: The logical name of the stream (used for logging only).
        :param stream: The stream to read from. This will typically a pipe
                       connected to the output stream of a subprocess.
        :param outbuf: The list to append the read lines to.
        """
        while True:
            s = stream.readline()
            if not s:
                break
            s = s.decode('utf-8').rstrip()
            outbuf.append(s)
            logger.debug('%s: %s' % (name, s))
        stream.close()