Process relative nameserver DNS record correctly
    
    Nameserver hostname passed to dnszone_add command was always treated
    as FQDN even though it was a relative DNS name to the new zone. All
    relative names were being rejected as unresolvable.
    
    Modify --name-server option processing in dnszone_add and dnszone_mod
    to respect FQDN/relative DNS name and do the checks accordingly. With
    this change, user can add a new zone "example.com" and let dnszone_add
    to create NS record "ns" in it, when supplied with its IP address. IP
    address check is more strict so that it is not entered when no forward
    record is created. Places misusing the option were fixed.
    
    Nameserver option now also accepts zone name, which means that NS and A
    record is placed to DNS zone itself. Also "@" is accepted as a nameserver
    name, BIND understand it also as a zone name. As a side-effect of this
    change, other records with hostname part (MX, KX, NS, SRV) accept "@"
    as valid hostname. BIND replaces it with respective zone name as well.
    
    Unit tests were updated to test the new format.
    
    https://fedorahosted.org/freeipa/ticket/3204