Try to reduce memory of MPI PPPM test
Try to reduce memory of MPI PPPM test

Use 2 ranks instead of 8, per Jens' suggestion.

refs #220

joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue