refactor: Fix staticcheck QF* issues

[alexandear]

The PR fixes issues reported by staticcheck under the QF* checks:

$ golangci-lint run
pkg/guestagent/kubernetesservice/kubernetesservice.go:143:4: QF1003: could use tagged switch on service.Spec.Type (staticcheck)
                        if service.Spec.Type == corev1.ServiceTypeNodePort {
                        ^
pkg/hostagent/dns/dns.go:83:3: QF1006: could lift into loop condition (staticcheck)
                if seen[cname] {
                ^
2 issues:
* staticcheck: 2

The if seen[cname] { break } condition was not covered by tests, so I added test cases for cyclic definitions.

[jandubois]

Thanks, LGTM