Allow the running of a subset of tests with a single command
From Evan: "A minor feature request: I've often wished there were a way to run a subset of the tests with a single command, like "sh run.sh dnssec autosign inline", but never got around to implementing it. While we've got the hood open, can we do that? If we support "make -j3 test-dnssec test-autosign test-inline", we can even take advantage of parallelization."