Parallel tests: Attempting to use an MPI routine after finalizing MPICH

The parallel tests return the error:

Attempting to use an MPI routine after finalizing MPICH

See reference:
https://www.unidata.ucar.edu/mailing_lists/archives/netcdf-hdf/2007/msg00108.html

Need to add an H5close() immediately before calling MPI_Finalize().

Might create a new CGNS API to avoid calling HDF5 directly.