Adding PMIx capability

1. Add new PMIx functionality to current slurm, So future compiled MPI programs can run on openmpi-3.1.4-pmix (PMIx only)

2. Ensure PMI and PMI2 libraries are available for existing MPI programs, So existing MPI programs will still run on openmpi-1.10.7-mlx and openmpi-3.1.4-mlx (PMI, PMI2 and PMIx)

3. Add a sym-link to current slurm with /opt/slurm-latest

[ec2-user@m3i001 ~]$ srun --mpi=list srun: MPI types are... srun: none srun: pmix_v3 srun: pmix srun: pmi2 srun: openmpi [ec2-user@m3i001 ~]$

changed the description

merged

mentioned in commit a03887de

mentioned in commit ffe9a936