Return the list of frozen states.

    CLI Example:

    .. code-block:: bash

        salt '*' freezer.list

def list_():
    '''
    Return the list of frozen states.

    CLI Example:

    .. code-block:: bash

        salt '*' freezer.list

    '''
    ret = []
    states_path = _states_path()
    if not os.path.isdir(states_path):
        return ret

    for state in os.listdir(states_path):
        if state.endswith(('-pkgs.yml', '-reps.yml')):
            # Remove the suffix, as both share the same size
            ret.append(state[:-9])
    return sorted(set(ret))