RFR (M): 8026046: add regression tests for ParallelGCThreads and ConcGCThreads flags

[Filipp Zhinkin]

Hi,

I would like to get couple reviews on test for ParallelGCThreads and 
ConcGCThreads flags.

Tests based jcmd's Thread.print output parsing.
Depending on used GC, ParallelGCThreads and ConcGCThreads values
it is trying to find appropriate number ofGC threads in thread dump.

Tests on ParallelGCThreads:
Test for G1 GC:
gc/arguments/TestG1GCParallelGCThreadsFlag.java
Test for GCs that use ParNew:
gc/arguments/TestParNewGCParallelGCThreadsFlag.java
Test for Parallel GC:
gc/arguments/TestPSGCParallelGCThreadsFlag.java
Test for all other GCs:
gc/arguments/TestNonParGCParallelGCThreadsFlag.java

Tests on ConcGCThreads:
Test for CMS GC:
gc/arguments/TestCMSGCConcGCThreadsFlag.java
Test for G1 GC:
gc/arguments/TestG1GCConcGCThreadsFlag.java
Test for all other GCs:
gc/arguments/TestNonConcGCConcGCThreadsFlag.java

Bug ID:  https://bugs.openjdk.java.net/browse/JDK-8026046
Webrev:  http://cr.openjdk.java.net/~kshefov/8026046/webrev.00/
Testing: manual on local host and automated on various platforms.

Thanks,
Filipp.