Return a list of all directories on the master

def dir_list(load):
    '''
    Return a list of all directories on the master
    '''
    if 'env' in load:
        # "env" is not supported; Use "saltenv".
        load.pop('env')

    ret = []

    if 'saltenv' not in load:
        return ret

    saltenv = load['saltenv']
    metadata = _init()

    if not metadata or saltenv not in metadata:
        return ret

    # grab all the dirs from the buckets cache file
    for bucket in _find_dirs(metadata[saltenv]):
        for dirs in six.itervalues(bucket):
            # trim env and trailing slash
            dirs = _trim_env_off_path(dirs, saltenv, trim_slash=True)
            # remove empty string left by the base env dir in single bucket mode
            ret += [_f for _f in dirs if _f]

    return ret