HDF5/MPI compatibility

Latest version of OpenMPI seems to be incompatible with HDF5 unless compiled with custom flag.

E-mail from @schni follows:

While installing Turtle on my private computer over the weekend I had the problem that newer versions of OpenMPI (>=3.0) are not compatible with the HDF5 library build with the --enable-parallel flag. Maybe we should include that in the README. The fixes are to install an older version of OpenMPI or build a newer version wtith the "--enable-mpi1-compatibility" flag set.

Quick browsing of HDF5 website does not yield an explicit dependency on a particular MPI standard.

@mjr, how flexible is the CI configuration here? Would it be feasible to test different versions of HDF5 and/or MPI? For instance I only use HDF5 1.8.x as far as I know, I think turtle actually failed with 1.10.x when I last tried it (it was still bfps at the time).