Reboots the device.

    Args:
        target_mode: Normal reboot when unspecified (or None). Can specify
            other target modes, such as 'recovery' or 'bootloader'.
        timeout_ms: Optional timeout in milliseconds to wait for a response.
    Returns:
        Usually the empty string. Depends on the bootloader and the target_mode.

def reboot(self, target_mode=None, timeout_ms=None):
    """Reboots the device.

    Args:
        target_mode: Normal reboot when unspecified (or None). Can specify
            other target modes, such as 'recovery' or 'bootloader'.
        timeout_ms: Optional timeout in milliseconds to wait for a response.
    Returns:
        Usually the empty string. Depends on the bootloader and the target_mode.
    """
    return self._simple_command('reboot', arg=target_mode,
                                timeout_ms=timeout_ms)