add pmi2 and pmix module, refactor openmpi-pmi2/x module, fix issue #151

[dingp]

No description provided.

[dingp]

We might include /etc/libibverbs.d bind mount into pmi2/x module, and remove openmpi-pmi2/x module.

In the case of the container with the whole compatible networking stack built-in, /etc/libibverbs.d is not needed, but doing a bind-mount is also harmless.

[brandongc]

Overall looks good, I have a few comments which are maybe a little outside the scope of this particular MR.

Why is /etc/libibverbs.d needed at all on the system?

Also, PALS is not relevant for Perlmutter.

There is a lack of parity on pmi2 and pmix Slurm variables (another candidate for factoring out).

Several of the /dev items are ok, but should be migrated to CDI.