Create a separate MLNX_OFED definition file (layer) apart from MPI

Until now, all base OS + MPI naked-singularity definition files also
included the Mellanox OFED drivers, libraries, and other dependencies
required to run MPI-based applications from the containers over
Infiniband (IB) on SDSC HPC systems. In order to provide additional
flexability and modularity to the naked-singularity definition file
dependency chain, we will now seperate out the installation of the
MLNX_OFED distribution from any MPI distributioni moving forward. i.e.,
there will be a definition file (layer) for each OS + MLNX_OFED
combination we choose to support.