test-driver: Allow configuring delay for send_{key,chars}

        with self.nested("waiting for {} to appear on tty {}".format(regexp, tty)):

            retry(tty_matches)

    def send_chars(self, chars: str) -> None:

    def send_chars(self, chars: str, delay: Optional[float] = 0.01) -> None:

        with self.nested("sending keys ‘{}‘".format(chars)):

            for char in chars:

                self.send_key(char)

                self.send_key(char, delay)

    def wait_for_file(self, filename: str) -> None:

        """Waits until the file exists in machine's file system."""

                if matches is not None:

                    return

    def send_key(self, key: str) -> None:

    def send_key(self, key: str, delay: Optional[float] = 0.01) -> None:

        key = CHAR_TO_KEY.get(key, key)

        self.send_monitor_command("sendkey {}".format(key))

        time.sleep(0.01)

        if delay is not None:

            time.sleep(delay)

    def send_console(self, chars: str) -> None:

        assert self.process