RFR: 8038481: CMM Testing: Min/MaxHeapFreeRatio flags should be manageable through the API

[Andrey Zakharov]

Hi, here is backport against
  http://hg.openjdk.java.net/hsx/jdk7u/hotspot
of early pushed to
  http://hg.openjdk.java.net/jdk9/hs-gc/hotspot
tests for Min/MaxHeapFreeRatio flags. The main reason of another review 
- patch didn't patch clearly - TEST.groups is absent in jdk7 branch.
webrev: http://cr.openjdk.java.net/~jwilhelm/8038481/webrev.01/
bug: https://bugs.openjdk.java.net/browse/JDK-8038481
Thanks.