PHD: support parameterized test cases #174
Description
Some test cases lend themselves very well to parameterization: if I launch an instance with X CPUs and Y CPU topology, then I expect the guest to see X and Y represented in such-and-such a way in the output from such-and-such commands, for a range of values of X and Y. There are some parameterized testing crates in the broader ecosystem, but I'm not sure any of them are applicable to freestanding test runners like PHD, so we might have to roll our own parameterization mechanism here, e.g. as an extension to the #[phd_testcase] macro.