Validate IPv6 support.

[Lukasa]

According to @fredthomsen in #164, we have a number of places where we parse hostnames/ports that probably won't work when using explicit IPv6 addresses. We should fix that logic in those places and add tests to validate that IPv6 behaves appropriately.

[fredthomsen]

Started looking at where this is done. So far I only see it in the constructors and the CLI, so this may be rather simple.

[fredthomsen]

Was looking through all open issues and noticed this was still here. I believe we covered this with #172 and can be closed.

[Lukasa]

Good spot @fredthomsen, thanks!