improve "make test" to run faster and be more portable

After a CMake build, "make test" seemed to hang on the login node. I dropped this from the build instructions for now. If there really is a hang, figure out why and how to resolve it. If there is not, consider adding this back as a way for users to test their install.

After trying again, I found that it might just take tens of seconds per test. It just takes a long time to complete, especially since there are 20+ tests and growing. Can we speed that up?

Also, on checking the code, I see we're using "-p pdebug" for srun jobs, which is a LLNL-ism. If we want others outside of LLNL to run these tests, we should find a way to generalize them.