Host specification does not seem to support ipv6 host format

[testn]

Take a look at https://www.ietf.org/rfc/rfc2732.txt for more detail.

[hornc]

FWIW, when I made changes for #420 I was only looking at IPv4 host definitions too. The underlying RFCs that json schema references I think are pre ipv6?, and the Swagger docs made no mention of ipv6 either, so this feels new, but 👍 for adding support. The docs should be updated too.

[fehguy]

Tagging this under #560

[fehguy]

see #646. We will support ipv6 via documentation updates.