Do not load invalid zones.
    
    Without this patch, it was possible to load an invalid zone without
    proper SOA or NS records because the fake SOA and NS records allowed
    checks in dns_zone_load() to pass.
    
    With this patch, no fake SOA or NS records are created and
    dns_zone_load() is not called before end of the initial synchronization.
    
    See the function ldapdb_associate() in ldap_driver.c and it's comments.
    
    Signed-off-by: Petr Spacek <pspacek@redhat.com>