Use full MPI library for mpi-serial tests #2497
Description
As discussed in CSEG we want to remove the use of mpi-serial in our tests and simulations. This is largely because modern MPI libraries allow you to link with the MPI library but still run serially WITHOUT using mpirun (mpiexec, mpibind, or any of the other flavors).
This depends on getting the mpirun update in cime here:
Or doing this explicitly for Derecho and Izumi in ccs_config.