test: shift default tests to use json-mirror and move nvd tests to network job?

[terriko]

As mentioned in #4111 , our regular test jobs currently don't call the mirror (but they do call out to NVD directly). There are mirror tests in the network-mayfail job.

I think given that --nvd json-mirror is now our default setting as of 3.3, we may want to swap things so that we have at least one mirror test in the short test job (if there's a reasonable way to do that given our current caching setup; there may not be), and we may need to move one or more of the tests currently using nvd to the network-mayfail job to compensate.