RFR: 8163413: gc/metaspace/TestMetaspacePerfCounters failure

[Stefan Johansson]

Hi,

Please review this test fix for:
https://bugs.openjdk.java.net/browse/JDK-8163413

Webrev:
http://cr.openjdk.java.net/~sjohanss/8163413/hotspot.00/

Summary:
The test failure is most likely caused by getting a GC in between the 
calls to get the perf counter values. Since the values are updated 
during a GC this might cause the values to break the assert conditions. 
To avoid this my fix checks the number of GCs that have been done before 
and after getting the values and only proceeds to doing the assertions 
if no GC occurred.

Testing:
* Verified test both locally and with RBT.

Thanks,
Stefan