List the files that belong to a package.

    CLI Examples:

    .. code-block:: bash

        salt '*' pkg.file_list nginx

def file_list(package, **kwargs):
    '''
    List the files that belong to a package.

    CLI Examples:

    .. code-block:: bash

        salt '*' pkg.file_list nginx
    '''
    ret = file_dict(package)
    files = []
    for pkg_files in six.itervalues(ret['files']):
        files.extend(pkg_files)
    ret['files'] = files
    return ret