[sh/jdk8u] RFR Shenandoah: properly deallocates class loader metadata

[Zhengyu Gu]

The problem was discovered when running vmTestbase tests, where 
Shenandoah fails following tests:

vmTestbase/nsk/jvmti/RedefineClasses/StressRedefineWithoutBytecodeCorruption/TestDescription.java
vmTestbase/nsk/jvmti/RedefineClasses/StressRedefine/TestDescription.java 
 
vmTestbase/vm/runtime/defmeth/scenarios/Stress_redefine/TestDescription.java

It appears to be 8u specific problem, where it handles class loader 
metadata differently. Let's mirror G1 on how metadata is handled.


Webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/sh-8u-metadata-clean/webrev.00/index.html

Test:
   hotspot_gc_shenandoah
   vmTestbase tests that no longer fail after patch.

Thanks,

-Zhengyu