mpiCheckPhaseHook: use low-level env HWLOC_XMLFILE in all MPI implementations

HWLOC_XMLFILE is lower-level than PRTE_MCA_hwloc_use_topo_file.
Setting PRTE_MCA_hwloc_use_topo_file require processes managed by prterun/mpiexec.
While setting HWLOC_XMLFILE will always work in sandbox environment.
This commit fix the annoying error message
"[hwloc/linux] failed to find sysfs cpu topology directory, aborting linux discovery."
When running mpi4py related python tests not managed by mpiexec.

pkgs/by-name/mp/mpiCheckPhaseHook/mpi-check-hook.sh

···
       # The solution is to use a preset cpu topology file and disable ucx model.
 
       # Disable sysfs cpu topology directory discovery.
-      export PRTE_MCA_hwloc_use_topo_file="@topology@"
+      export HWLOC_XMLFILE="@topology@"
       # Use the network model ob1 instead of ucx.
       export OMPI_MCA_pml=ob1
       ;;
···
     MVAPICH)
       # Disable CPU pinning
       export MV2_ENABLE_AFFINITY=0
+      # Disable sysfs cpu topology directory discovery.
+      export HWLOC_XMLFILE="@topology@"
       ;;
   esac