WL4189 Cap the autodetected parallelism value to 8

mysql-test/mysql-test-run.pl

@@ -279,6 +279,7 @@ sub main {
     for my $limit (2000, 1500, 1000, 500){
       $opt_parallel-- if ($sys_info->min_bogomips() < $limit);
     }
+    $opt_parallel= 8 if ($opt_parallel > 8);
     $opt_parallel= $num_tests if ($opt_parallel > $num_tests);
     $opt_parallel= 1 if ($opt_parallel < 1);
     mtr_report("Using parallel: $opt_parallel");