AD: process non-posix nested groups w/o tokenGroups
    
    When initgr is performed for AD not supporting tokenGroups, do not
    filter out groups without gid attribute or with gid equal to zero.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2343
    
    Reviewed-by: Michal Židek <mzidek@redhat.com>
    (cherry picked from commit 981bf55532fbec91a106f82d7daf32094c76dfe0)