Add processor and processor_affinity property to tests

[bartgol]

Without these properties, when running multiple tests at once, all ranks collapse on the same cores (MPI does not check if other MPI jobs are running, so it usually takes cores 0-N). With the properties set, however, ctest ensures tests are run on different cores and don't overload cores.

NOTE: PROCESSOR_AFFINITY TRUE ensures no 2 tests can share cores, while PROCESSORS XYZ ensures that, when doing ctest -j N a test "consumes" XYZ of the N cores (without the property, ctest assumes that the test consumes 1 core).