introduce IP address normalization

It turns out that genreport and dnspython use different string formats
for IPv6 addresses and this is causing problems in certain special
cases.

Thanks to Sven Van Dyck <svenvd@dnsbelgium.be> for reporting this!
2 jobs for <span class="ref-name">ipaddr_norm</span> in 3 minutes and 50 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #221142
docker
lint

00:00:28

passed #221143
docker
test

00:03:50