Copies all the saved arguments (from saveArgs) to the startup file
so that when the box reboots, the arguments are executed.
function prepareArgsForReboot() {
    const deferred = q.defer();
    let startupScripts;
    let startupCommands;
    let startupCommandsChanged;

    const STARTUP_DIR = '/config/';
    const STARTUP_FILE = `${STARTUP_DIR}startup`;
    const REBOOT_SIGNAL = ipc.signalBasePath + signals.REBOOT;

    if (!fs.existsSync(STARTUP_DIR)) {
        logger.debug('No /config directory. Skipping.');
        deferred.resolve();
        return deferred.promise;
    }

    try {
        startupCommands = fs.readFileSync(STARTUP_FILE, 'utf8');
    } catch (err) {
        logger.warn('Error reading starup file.');
        deferred.reject(err);
        return deferred.promise;
    }

    try {
        startupScripts = fs.readdirSync(REBOOT_SCRIPTS_DIR);
    } catch (err) {
        logger.warn('Error reading directory with reboot args.');
        deferred.reject(err);
        return deferred.promise;
    }

    // Make sure there's a new line at the end in case we add anything
    startupCommands += EOL;

    // If we just rebooted, make sure the REBOOT signal file is deleted
    // so scripts don't think we need to reboot again
    if (startupCommands.indexOf(REBOOT_SIGNAL) === -1) {
        startupCommandsChanged = true;
        startupCommands += `rm -f ${REBOOT_SIGNAL}${EOL}`;
    }

    startupScripts.forEach((script) => {
        const fullPath = REBOOT_SCRIPTS_DIR + script;
        if (startupCommands.indexOf(fullPath) === -1) {
            startupCommandsChanged = true;
            startupCommands += `if [ -f ${fullPath} ]; then${EOL}`;
            startupCommands += `    ${fullPath} &${EOL}`;
            startupCommands += `fi${EOL}`;
            startupCommands += EOL;
        }
    });

    if (startupCommandsChanged) {
        try {
            fs.writeFileSync(STARTUP_FILE, startupCommands);
        } catch (err) {
            logger.warn('Failed writing startup file', STARTUP_FILE, err);
        }
    }

    deferred.resolve();

    return deferred.promise;
}