* zoltan: only add gussed MPI libs if no MPI wrappers are used
- if MPI-wrappers are used for compilation, we can assume that
linking works without manually specifying MPI libs
(guessing may result in wrong libs, cf. #8979)
- thus, only guess the NPI libs and add them explicitly if no
MPI-wrappers are used
- use llnl.util.filesystem.find_libraries instead of a locally
defined routine to guess the MPI libs if needed
(cf. #8979)
* zoltan: rely on MPI-wrappers to know the required MPI libs
a02cf107b5