WIP: Place brackets around the hostname

[WilliamDEdwards]

When setting $apiip to an IPv6 address, requests to the PowerDNS API fail with cURL error 0 and an empty curl_error. This is because cURL doesn't understand we're working with an IPv6 address. This should be fixed by placing brackets around the address.

This PR is not finished. AFAIK, we don't have to check the address family, because placing brackets around an IPv4 address works. However, we still don't know whether we're dealing with a hostname or not.