Check if launched with mpirun
Check if launched with mpirun

Error out if the users launches with mpirun in a ENABLE_MPI=off build.
This isn't foolproof as there is no real way to tell if we were launched
by mpirun or some other launcher. But I've got standard OMPI and MVAPICH
stacks covered which will save many hoomd users from annoying errors.

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