WIP: fix for issue 17790

[dezmodue]

As discussed in the kOps meeting yesterday, given a pod with HostNetwork and AnnotationNameDNSInternal we can use directly the pod IP to create the DNS names. Once this patch is applied the dns-controller correctly creates DNS entries for kops-controller and api internal endpoints:

I1205 10:18:18.568880       1 dnscontroller.go:586] Adding DNS changes to batch {A kops-controller.internal.ernie.example.com.} [10.101.18.248 10.101.53.90 10.101.64.234]

I1205 10:18:18.568937       1 dnscontroller.go:586] Adding DNS changes to batch {A api.internal.ernie.example.com.} [10.101.18.248 10.101.53.90 10.101.64.234]
and
❯ kubectl get nodes -o wide | awk '/control/ {print $6}'
10.101.53.90
10.101.18.248
10.101.64.234

Ping @justinsb as requested

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[hakman]

/ok-to-test /assign @justinsb

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[dezmodue]

Hi, I was wondering if the same issues are present for AnnotationNameDNSExternal as the dns-controller might create DNS entries that point to IPs that are associated with the node but not the pod itself (I cannot verify this). I could extend the PR to adopt the same logic also for AnnotationNameDNSExternal if that makes sense. @justinsb

[dezmodue]

We are running this fix in our clusters and we've seen no issues over the last couple weeks. The time for a node to join the cluster is now consistently and reliably around 1 minute while before it could take over 10 minutes in the worst cases.

[dezmodue]

@justinsb @hakman I added the suggested changes and some additional tests

1. If the pod has a single IP just use that and avoid any calls to API
2. Set record type correctly for IPv4 and IPv6