mpi/tests/Makefile.am: run tests on 4 processes

mpi/tests/Makefile.am

@@ -19,9 +19,9 @@ CCLD=$(MPICC)
 
 if STARPU_MPI_CHECK
 if STARPU_HAVE_AM111
-LOG_COMPILER	 	=	$(MPIEXEC) -np 2
+LOG_COMPILER	 	=	$(MPIEXEC) -np 4
 else
-TESTS_ENVIRONMENT 	=	$(MPIEXEC) -np 2
+TESTS_ENVIRONMENT 	=	$(MPIEXEC) -np 4
 endif
 TESTS			=	$(check_PROGRAMS)
 endif