Save the register to msgpack files

def save_reg(data):
    '''
    Save the register to msgpack files
    '''
    reg_dir = _reg_dir()
    regfile = os.path.join(reg_dir, 'register')
    try:
        if not os.path.exists(reg_dir):
            os.makedirs(reg_dir)
    except OSError as exc:
        if exc.errno == errno.EEXIST:
            pass
        else:
            raise
    try:
        with salt.utils.files.fopen(regfile, 'a') as fh_:
            salt.utils.msgpack.dump(data, fh_)
    except Exception:
        log.error('Could not write to msgpack file %s', __opts__['outdir'])
        raise