This will prevent indefinitely-hanging requests in case some service or middle box is malfunctioning.
Fix vet errors and lint warnings
Add vet to CI check
Only get issuer certificate if it would be used
No need to make a GET request if the OCSP server is not specified in leaf certificate
Fix CI tests
Make tests verbose
* Gets a list of all authoritative nameservers by looking up the NS RRs for the root domain (zone apex)
* Verifies that the expected TXT record exists on all nameservers before sending off the challenge to ACME server
We can ask the OS resolver for the IP of Google's public anycast DNS.
No need to "bootstrap" with literal IP address. The OS resolver knows
best about IPv4 ./. IPv6.
Mostly fixes#88.
