Fix/remove broken integration-cli IPv6 tests

[robmry]

- What I did

Found two integration-cli tests that didn't run, because the "requires IPv6" test they used was wrong (it'd only return true on a host with no IPv6), and sorted that out.

- How I did it

Fixed one test, deleted the other, deleted associated/broken helper functions - see the individual commit messages.

- How to verify it

It's tests.

- Description for the changelog