Make relative names in AXFR into FQDN

[niclan]

In the zonetransfer provider the RHS of a CNAME may be a relative name not necessarily a FQDN. So for example

www.example.com CNAME webserver

instead of

www.example.com CNAME webserver.example.com.

Note significant ending . in the second example. This PR makes relative names into FQDNs.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[niclan]

I was unable to get this into a list comprehension, sorry.

[imnotbrandon]

Hi, thanks for the contribution!

Whilst testing this, I've discovered that false negatives are produced because we don't recursively resolve records.

This isn't an issue introduced by your code, but I thought you should be aware given the context. I've already got a working fix so I'll merge that in separately once it's properly tested.