humility test suite could be less needlessly cruel

[hawkw]

Running the Humility test suite is one of the most unkind things I've done to my poor laptop: it takes about five minutes to run, and pins every CPU core at 100% for the entire duration:

It seems like this is because the complexity of the test suite is multiplicative: it's the number of cores times the number of commands we run. This means that adding a new command increases the total size of the test suite by len(cores), and adding a new core increases the total size of the test suite by len(commands).

There's probably a way to make this a bit less of a brutal dev machine torture test: in at least some cases, such as counters, a command is only "interesting" to run on newer cores that contain the structures the command interprets. Running humility counters on any core except for the one I added specifically to test the counters will just result in humility error: no counters found. So, we probably don't need to run the several different counters commands in the test suite against every core we currently test with. If we added a notion of "only run this command against these cores" to the test framework, we could make it a little less painful to run.