Cleanup dns client tests. (#567)
Cleanup dns client tests. (#567)

* Cleanup dns client tests.

Remove panics and improve readability.

* Put the `return`s back as they matter

* Remove another panic

daviddrysdale/certificate-transparency-go,google/certificate-transparency-go,google/certificate-transparency-go,RJPercival/certificate-transparency-go,google/certificate-transparency-go,daviddrysdale/certificate-transparency-go,daviddrysdale/certificate-transparency-go,RJPercival/certificate-transparency-go,RJPercival/certificate-transparency-go