Simplifying the test cases

[kaanolgu]

The test cases have lots of common calls which are shared by many tests. We could generate a test_common.f90 or test_base.f90
to store these common routines for all of the tests. For example this is shared by the tests:

  subroutine initialise_mpi()
    call MPI_Init(ierr)
    call MPI_Comm_rank(MPI_COMM_WORLD, nrank, ierr)
    call MPI_Comm_size(MPI_COMM_WORLD, nproc, ierr)

    if (nrank == 0) print *, 'Performance benchmark with', nproc, 'ranks'

    pnext = modulo(nrank - nproc + 1, nproc)
    pprev = modulo(nrank - 1, nproc)
  end subroutine initialise_mpi 

This way we could reduce the complexity of standalone tests