mpirun on Aimos

[RPIFisherman]

We need to let the user provide the commands and arguments to run and control MPI jobs used in test/CMakeLists.txt (after PR #10 is merged).

This is an old problem I mentioned in May: when I want to run the tests on Aimos, if I do:
mpirun --bind-to core -np 1 ctest --test-dir buildPolyMPO-GPU/
on Aimos, once the first test called finalized, the other tests will just freeze. So I need to call mpirun every time.
This evening when I tried to run the tests on Perlmutter, I found that there is no mpirun on Perlmutter, so I added a new commit to check if there is mpirun: 994e2b5
This is just a temporary solution to pass all the tests on all the environments (Cranium, Perlmutter, and Aimos).
I don't know much about the ctest and how to use mpirun with it. I need some help on that.

Originally posted by @RPIFisherman in #10 (comment)