RFR: 8287596: Reorg jdk.test.lib.util.ForceGC [v4]

[Xue-Lei Andrew Fan]

> This is a follow up update per comments in [JDK-8287384 PR](https://github.com/openjdk/jdk/pull/8907).  The tier1 and tier2 test in open part looks good to me.  Please help to run Mach5 just case the closed test cases are impacted.

Xue-Lei Andrew Fan has updated the pull request incrementally with one additional commit since the last revision:

  rollback is not in this branch

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8979/files
  - new: https://git.openjdk.java.net/jdk/pull/8979/files/a8768e09..4a80db95

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8979&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8979&range=02-03

  Stats: 58 lines in 1 file changed: 17 ins; 24 del; 17 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8979.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8979/head:pull/8979

PR: https://git.openjdk.java.net/jdk/pull/8979