NSS: Use right domain for group members with fq names
    
    If we query group from subdomain it can contain users from different domains.
    All members from subdomain have fully qualified name, but member from main
    domain aren't. In function fill_members, we extracted name and domain with
    function fill_members. Later, we called function sss_fqname the first time
    with queried group domain and the second time with parsed domain.
    It caused following error in nss responder:
    
    [fill_members] (0x0040): Failed to generate a fully qualified name for member
      [user2_dom1@sssdad_tree.com] of group [group2_dom2@sssdad_tree.com]! Skipping
    
    The test test_nss_getgrnam_mix_dom_fqdn passed, because name of main domain
    and name of subdomain had the same length, Therefore there was not problem
    in function fill_members with calling sss_fqname with different domains.
    This patch also changes name of subdomain to prevent such problems in future.
    
    Reviewed-by: Pavel Reichl <preichl@redhat.com>