Return a set of services that are installed but disabled

    CLI Example:

    .. code-block:: bash

        salt '*' service.get_disabled

def get_disabled():
    '''
    Return a set of services that are installed but disabled

    CLI Example:

    .. code-block:: bash

        salt '*' service.get_disabled
    '''
    (enabled_services, disabled_services) = _get_service_list(include_enabled=False,
                                                              include_disabled=True)
    return sorted(disabled_services)