RFR: 8080345: With perm gen gone, perfdata counter sun.gc.policy.generations should be 2, not 3

[Erik Helin]

Hi all,

I picked up this patch that Ramki posted quite a while ago: when I 
updated the tooling I forgot to update the performance counter 
'sun.gc.policy.generations'. This patch takes care of this problem, 
sun.gc.policy.generations now reports 2 instead of 3.

I also added a test that verifies the fix. As part of adding the test I 
had to move the test support classes PerfCounter.java and 
PerfCounters.java from test/hotspot/jtreg/gc/metaspace to 
test/hotspot/jtreg/gc/testlibrary.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8080345

Patch:
http://cr.openjdk.java.net/~ehelin/8080345/00/

Testing:
- hs tier1-5
- newly added jtreg test
- jstat and jstatd tests under test/jdk/sun/tools/jstat{d}

Thanks,
Erik