List directories of specified path.
    :param fs_id: The filesystem identifier.
    :param path: The path where to start listing the directory content.
    Defaults to '/' if not set.
    :type path: str | bytes
    :param depth: The number of steps to go down the directory tree.
    :type depth: int | str
    :return: The names of the directories below the specified path.
    :rtype: list