Reduce test time in valgrind runs

tests/microbenchs/tasks_size_overhead.c

@@ -191,6 +191,13 @@ int main(int argc, char **argv)
 	unsetenv("STARPU_NCPU");
 #endif
 
+#ifndef STARPU_QUICK_CHECK
+	if (STARPU_RUNNING_ON_VALGRIND) {
+		factortime = 16;
+		cpustep = 2;
+	}
+#endif
+
 	parse_args(argc, argv);
 
 	float *buffers[total_nbuffers?total_nbuffers:1];