Test harness needs a more flexible testname white/blacklist argument

[bblum]

I'm trying to narrow down which subset of core::task's tests cause deadlock, and I have to keep recompiling everything with different sets of tasks commented out, because a "just one substring match" whitelist is not flexible enough to search arbitrary subsets of the tests.

It'd be great if the test harness accepted multiple testname arguments to whitelist, or a regex, or a blacklist, etc.

[Aatch]

Nominating for production ready

[graydon]

just a bug, removing milestone/nomination.

[huonw]

Triage visit; still a plain substring match.

Regex support would be neat, but is blocked on #3591.

[huonw]

Triage visit; still a plain substring match.

And still blocked on #3591.