Skip all tests if DNS lookup fails
Skip alternate endpoints on failed connection

We try these endpoints in order:

   https://hostname.example/.well-known/host-meta.json
   https://hostname.example/.well-known/host-meta
   http://hostname.example/.well-known/host-meta.json
   http://hostname.example/.well-known/host-meta

If the first HTTPS one fails to connect, there's no use try to connect
to the second HTTPS one. Same with HTTP.

This change fails early.