Add more tests

[certik]

Add more MPI tests

[gxyd]

To add more tests, we can take a look at: https://docs.open-mpi.org/en/v5.0.x/man-openmpi/man3/index.html, which lists for us a lot of MPI subroutines, one can check which subroutines aren't present in any of the tests in standalone tests file, and create a test with that subroutine call in it.

[gxyd]

Subroutines/objects from POT3D which require standalone tests are:

• MPI_Bcast
• MPI_Comm_split_type
• MPI_Cart_shift
• MPI_Allgather
• MPI_Barrier
• MPI_Isend
• MPI_Irecv
• MPI_Waitall
• MPI_PROC_NULL
• MPI_STATUSES_IGNORE
• MPI_Recv
• MPI_Ssend