yamlify `arg` and ensure it's outermost datatype is a list

def _parse_args(arg):
    '''
    yamlify `arg` and ensure it's outermost datatype is a list
    '''
    yaml_args = salt.utils.args.yamlify_arg(arg)

    if yaml_args is None:
        return []
    elif not isinstance(yaml_args, list):
        return [yaml_args]
    else:
        return yaml_args