[ofiwg] Coverity coverage of new providers

[Hefty, Sean]

> It looks like we're not building the following providers for Coverity
> testing coverage:
> 
> - GNI
> - PSM2

I believe this is doable.  Copying Jianxin.

> - MXM

This is more difficult.  I'm able to build against mxm on my system, but I had to manually extract out the library files from an installation package.  I don't think there's an open source solution for mxm.