The `oil_skip` test option was added for tests that don't work under OIL
but do work under OID. However, we now have two classes of `oil_skip`ped
tests: those that could be fixed, and those that will never work.
Increase clarity by not generating the tests which do not make sense at
all, leaving us with a cleaner set of skipped (and fixable) tests.
The extern repos are currently cloned with SSH. This means that
attempting to clone them on a system that doesn't have an SSH key which
GitHub accepts fails. Change them to HTTPS as they're read only anyway.
