OMPI/v2.x is missing pmix2x component

[artpol84]

As far as I recall there was an agreement that OMPI v2.1.0 will have PMIx v2.0.
However not this is not a case:
https://github.com/open-mpi/ompi/tree/v2.x/opal/mca/pmix

We need to identify proper commits and port them from master.

[artpol84]

@rhc54 @jladd-mlnx @jsquyres @hppritcha

[jladd-mlnx]

Closing this. Duplicates #2072