RFR: 8200102: NativeLibraryTest.java fails intermittently, unloaded count is not same as expected [v2]

[Brent Christian]

> Please review this fix for the intermittently-failing java/lang/ClassLoader/nativeLibrary/NativeLibraryTest.java.
> 
> The change replaces System.gc()+sleep() with the more robust gcAwait() mechanic used elsewhere in the test base, [as pointed out by Martin](https://bugs.openjdk.java.net/browse/JDK-8200102?focusedCommentId=14382648&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14382648)(thanks!).
> 
> The new version of the test passes 100 times out of 100 on the test farm.

Brent Christian has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into 8200102
 - Use existing ForceGC class in the test lib
 - Add gcAwait() mechanism

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1630/files
  - new: https://git.openjdk.java.net/jdk/pull/1630/files/a66308e8..a6d58148

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1630&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1630&range=00-01

  Stats: 10552 lines in 197 files changed: 6632 ins; 3120 del; 800 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1630.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1630/head:pull/1630

PR: https://git.openjdk.java.net/jdk/pull/1630