Correct sys thread filter to include fj pool. (#15)

* Correct sys thread filter to include fj pool.

* Actually, this is the 'default' common ForkJoinPool prefix on openjdk, let's use this.

Author: dweiss

randomizedtesting-jupiter/src/main/java/com/carrotsearch/randomizedtesting/jupiter/SystemThreadFilter.java

@@ -11,7 +11,7 @@
  */
 public class SystemThreadFilter implements Predicate<Thread> {
   private static final Pattern KNOWN_SUBSTRINGS =
-      Pattern.compile("(^ForkJoinPool\\.)|(Poller SunPKCS11)");
+      Pattern.compile("(^ForkJoinPool\\.commonPool)|(Poller SunPKCS11)");
 
   @Override
   public boolean test(Thread t) {