PYSSS: Re-add the pysss.getgrouplist() interface
    
    Related:
    https://pagure.io/SSSD/sssd/issue/3493
    
    Commit 0e211b8ba30c3adcdeef21ca1339b194cbfffb04 was supposed to remove
    only the parts of the pysss API that relate to the local domain. But it
    removed also the getgrouplist() method by accident. This method is very
    important to IPA, so we need to add it back.
    
    Reviewed-by: Alexander Bokovoy <abokovoy@redhat.com>