Adapt TheFlintstonesTest to IPv6 testing environments

[imonteroperez]

Highlights

• This PR adapts the execution of TheFlintstonesTest for IPv6 testing environments
• It makes feasible to use the overrided DNS as dns://[0:0:0:0:0:0:0:1]:32780

Testing done

• Tested via PCT under IPv4 and IPv6 environments and working as expected.

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[jtnord]

code appears to make some incorrect assumptions, and instead should switch on the type if InetAddress it obtains, or just not even bother and use the API

[jtnord]

I think this would break on IPv6 only hosts?
as you are getting an InetAddress, you can already know if you have a v4 or v6 address and react accordingly and do not use the system property.

e.g.

InetAddress inAddr = InetAddress.getByName(docker.getHost());
if (inAddr instanceof Inet6Address) {
 //...
 } else {
  /....
}

now if you want to do something based on a preference, you should be asking for all addresses (getAllByName()), and looking for the one according to the preference - but there may not be one... But YAGNI

or just stop building URLs by hand... and embrace the APIs
new URI("dns", null, docker.getHost()).getHostAddress(), docker.getDNSPort(), null, null, null).toASCIIString();

[imonteroperez]

Addressed in 7690fd7