Tests: DNS replace 192.0.2.0/24 with 198.18.0.0/15 range
    
    192.0.2.0/24 is IANA reserved address that should not be used. netaddr
    module check implemented for this address and IPA reject this address as
    invalid.
    198.18.0.0/15 is IANA reserved address for benchmark testing purpose, so
    we can safely use this network.
    
    http://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml
    
    https://fedorahosted.org/freeipa/ticket/5513
    
    Reviewed-By: Petr Spacek <pspacek@redhat.com>