Inconsistent MPI between the mgmt node and compute nodes

[chryswoods]

OpenMPI is installed on the mgmt node, but it is not installed on the compute nodes. This means that users mistakenly believe that OpenMPI is available and usable, when it isn't.

I think it would be good to make the mgmt and compute nodes consistent. As MPI is very useful, I recommend that OpenMPI is installed on the compute nodes by default, so that a vanilla CitC can run MPI jobs with no extra configuration. This would also help with "module", as installing OpenMPI via yum also adds the OpenMPI module file to /etc/modulefiles, thereby ensuring that it is available and consistent across all nodes.

If this isn't added, then users need to add the following to their compute_image_extra.sh and rebuild the image;

sudo yum install -y openmpi