RFR: 8287384: Speed up ForceGC

[Xue-Lei Andrew Fan]

Hi,

May I have this test update reviewed?

The ForceGC could be enhanced by using smaller wait/sleep time, and shared cleaner.

Thanks,
Xuelei

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Commit messages:
 - 8287384: Speed up ForceGC

Changes: https://git.openjdk.java.net/jdk/pull/8907/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8907&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287384
  Stats: 21 lines in 1 file changed: 8 ins; 1 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8907.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8907/head:pull/8907

PR: https://git.openjdk.java.net/jdk/pull/8907