[8u] 8168682: jdk/test/java/lang/ClassLoader/forNameLeak/ClassForNameLeak.java fails with -Xcomp

[Zhengyu Gu]

I would like to backport this patch to OpenJDK8u for parity with Oracle 
8u281.

The original patch does not apply cleanly, has a lot of conflicts, but 
mainly due to line shifts, and can be resolved manually.

There are a couple of adjustments to the original patch.

1) ClasLoader.getPlatformClassLoader() (11u) -> 
ClassLoader.getSystemClassLoader() (8u)

2) JarUtils has different API in 8u, adjusted accordingly.

The original bug: https://bugs.openjdk.java.net/browse/JDK-8168682
The original patch: http://hg.openjdk.java.net/jdk/jdk/rev/64a52906b71f

8u webrev: http://cr.openjdk.java.net/~zgu/JDK-8168682-8u/webrev.00/

Test:
   ClassForNameLeak.java test passed on Linux x86_64 (fastdebug and release)

Thanks,

-Zhengyu