Deprecate the current OMPI-specific MPI_Info key definitions for
MPI_Comm_spawn and replace them with their PMIx equivalents. Issue a
deprecation/conversion warning as this is done. Also issue deprecation
warnings for options such as "ompi_non_mpi" that are no longer used.
Handle both cases where the user might pass either the PMIx attribute
name itself (e.g., "PMIX_MAPBY") or the string value of the attribute
(e.g., PMIX_MAPBY, which translates to "pmix.mapby"). This can only be
done for PMIx v4 and above, so protect that code.
Silence a couple of Coverity warnings and add a test along the way.
Signed-off-by: Ralph Castain <rhc@pmix.org>