make parthenon manager play nicely with other MPI libraries

[Yurlungur]

PR Summary

A downstream code wants to interface with PetSC, which also interacts with MPI via MPI init and finalize. This MR makes that interaction and only that interaction safe from Parthenon's perspective.

I haven't thought fully how we interact with other libraries so I don't know if we are safe to interop with, e.g., PetSC. Also in the grand scheme of things, what this downstream code wants to do with PetSC parthenon can do natively. So it might be an intermediate step.

That said, I think this at a minimum just makes parthenon a little safer and more robust.

PR Checklist

• Code passes cpplint
• New features are documented.
• Adds a test for any bugs fixed. Adds tests for new features.
• Code is formatted
• Changes are summarized in CHANGELOG.md
• Change is breaking (API, behavior, ...)
  • Change is additionally added to CHANGELOG.md in the breaking section
  • PR is marked as breaking
  • Short summary API changes at the top of the PR (plus optionally with an automated update/fix script)
• CI has been triggered on Darwin for performance regression tests.
• Docs build
• (@lanl.gov employees) Update copyright on changed files

[lroberts36]

LGTM. I guess it is still possible that some other code calls MPI_Initialize after Parthenon calls it, but I think this is the best we can do from our perspective.

[Yurlungur]

LGTM. I guess it is still possible that some other code calls MPI_Initialize after Parthenon calls it, but I think this is the best we can do from our perspective.

Yeah if all relevant codes have guards like this, then order won't matter. If only we are careful, then it will.