The cap_dns tests require Internet access. Currently they fail when
that's not available, which for CI purposes is undesirable. Let's
instead skip the tests if none of the non-casper name/addr lookups
succeed.
To that end:
- Convert the tests to ATF so that skipping is more natural.
- Break up the tests into separate test cases.
- If one of the system (i.e., non-casper) lookup functions fails, skip the test if all of them failed, otherwise fail the tests, since partial failure indicates something is flaky.