8151460: Metaspace counters can have inconsistent values

[Stefan Johansson]

Hi,

Please review this test-fix to avoid the problems described in:
https://bugs.openjdk.java.net/browse/JDK-8151460

Webrev:
http://cr.openjdk.java.net/~sjohanss/8151460/hotspot.00/

Summary:
Two of the metaspace perf-counter tests fails intermittently when run 
with -Xcomp. One reason this has been more frequent lately is a change 
to one of the tests that removed a System.gc() call. This call seems to 
be more important when running with -Xcomp. Having the System.gc() call 
is needed because the PerfCounters are only updated after a GC. And if 
any class loading/unloading happens after the call we can't do the 
assertions we are doing.

When doing this fix I also realized that one of the tests hadn't changed 
UseCompressedKlassPointers to UseCompressedClassPointers, both the 
command-line and the test-code used the old version so I updated this as 
well.

Testing:
The updated tests pass in RBT.

Thanks,
Stefan