MPI bug for MAC when writing lots of files

[kuberry]

We won't be fixing this error. If a user has Open MPI from before early 2018 (any version, I believe), a file description leak will prevent an application from writing more than ulimit number of times.

Details at:
open-mpi/ompi#4336

ulimit is usually 256, so this won't be a problem for many of our applications, but if you write output files at every timestep, you can see how this could easily become a problem.

Two ways to address it:

• reinstall Open MPI to a newer version, then reinstall NetCDF, etc...
  or
• Set ulimit -n 1024 or some other large number than the number of files you intend to write with one call of an executable.