RFR[XS] 8191747 [TESTBUG] runtime/appcds/DumpClassList.java and ProhibitedPackage.java fail on product bits

[Ioi Lam]

Hi,

Here's a fix for these two tests failing in product builds. The fix is 
to replace the use of debug flag PrintSystemDictionaryAtExit flag with 
-Xlog:class+load, which is available in product builds:

https://bugs.openjdk.java.net/browse/JDK-8191747
http://cr.openjdk.java.net/~iklam/jdk10/8191747-avoid-PrintSystemDictionaryAtExit-in-tests.v01/

Thanks
- Ioi