Send this command to the server and
        return a tuple of the output and the stderr.

        The format for parameters is:

        cmd (string): The command to send to the sever.

def sendline(self, cmd):
        '''
        Send this command to the server and
        return a tuple of the output and the stderr.

        The format for parameters is:

        cmd (string): The command to send to the sever.
        '''
        self.conn.sendline(cmd, self.linesep)

        # saw_prompt = False
        ret_stdout = []
        ret_stderr = []
        while self.conn.has_unread_data:
            stdout, stderr = self.conn.recv()

            if stdout:
                ret_stdout.append(stdout)
            if stderr:
                log.debug('Error while executing command.')
                ret_stderr.append(stderr)

            if stdout and self.prompt_re.search(stdout):
                break

        return ''.join(ret_stdout), ''.join(ret_stderr)