scripts: Wire --test-exclude through test harness

Add --test-exclude to process_common_args in test-util.sh and forward
it to the performance-metrics binary from run_metrics.sh.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

scripts/test-util.sh

@@ -122,6 +122,10 @@ process_common_args() {
             shift
             test_filter="$1"
             ;;
+        "--test-exclude")
+            shift
+            test_exclude="$1"
+            ;;
         "--build-guest-kernel")
             build_kernel=true
             ;;