Certain MPI types were not being recognized by mpi4py.

It is not clear what the issue was. Using OpenMPI, MPI.INT64_T
and MPI.BOOL were not working. Changed the code such that the
types pointed by mpi4py are used directly rather than assuming
the type.

Change-Id: If98f64bfd7ecb24538b9a8ac7ca60105a5062ca6
Merge topic 'fix-mpi-types' into master

8b73e3b8 Certain MPI types were not being recognized by mpi4py.