Provide a KokkosCommInitialize

[cedricchevalier19]

It must enforce a correct calling order for MPI_Init and Kokkos::initialize.

It should also handle special Kokkos arguments:

Another pretty annoying thing that we have to do is to avoid passing --help to non-zero ranks, as otherwise Kokkos would print help on all ranks. We do it like this:

  // Strip "--help" and "--kokkos-help" from the flags passed to Kokkos if we
  // are not on MPI rank 0 to prevent Kokkos from printing the help message
  // multiply.
  if (comm_rank != 0)
  {
    auto *help_it = std::find_if(argv, argv + argc, [](std::string const &x) {
      return x == "--help" || x == "--kokkos-help";
    });
    if (help_it != argv + argc)
    {
      std::swap(*help_it, *(argv + argc - 1));
      --argc;
    }
  }
  Kokkos::initialize(argc, argv);

Originally posted by @aprokop in #53 (comment)

[dssgabriel]

Tracking issue for #68?

Note that with the MPI Sessions model, we do not require users to call MPI_Init before our own initialization.

[cedricchevalier19]

#68 is more than that: here, it is a simple function that does not necessarily use sessions.