test/mpi/f08: switch to 'use mpi_f08' in util

Switch to 'use mpi_f08' in MTest_Finalize and MTestSpawnPossible

Author: Gregor Corbin

test/mpi/util/mtest_f08.f90

@@ -22,7 +22,7 @@ subroutine MTest_Init( ierr )
         end
 !
         subroutine MTest_Finalize( errs )
-        use mpi
+        use mpi_f08
         integer errs
         integer rank, toterrs, ierr
 
@@ -108,7 +108,7 @@ subroutine MTestPrintErrorMsg( msg, errcode )
         end
 
         subroutine MTestSpawnPossible( can_spawn, errs )
-        use mpi
+        use mpi_f08
         integer can_spawn
         integer errs
         integer(kind=MPI_ADDRESS_KIND) val