RFR: 8375485: Tests in vmTestbase/nsk are failing due to missing class unloading after 8373945 [v3]

[SendaoYan]

> Hi all,
> 
> This PR make 2 changes which make test more rubustness:
> 
> 1. Add max 10 times tries which removed by JDK-8342659, this will make test more steady after JDK-8373945. vmTestbase/nsk/jvmti/CompiledMethodUnload/compmethunload001/TestDescription.java fails before this PR, run passed after this PR with fastdebug build.
> 2. test/hotspot/jtreg/vmTestbase/nsk/jvmti/scenarios/events/EM02/em02t003.java try to invoke thread and do not wailt the thread run finish unload the class immediately. This PR wait util the thread is non alive, and wait more 2 senonds to make sure the thread exit completely. This will make test more robustness, before this PR vmTestbase/nsk/jvmti/scenarios/events/EM02/em02t003/TestDescription.java fails probability 1/50, after this PR test run all passed 10k times.
> 
> Additional testing:
> 
> - [x] All tests touched test by JDK-8373945 with relase build
> - [ ] All tests touched test by JDK-8373945 with fastdebug build

SendaoYan has updated the pull request incrementally with one additional commit since the last revision:

  Remove unnecessary runtime.gc() afer classloader has been reclaimed

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29285/files
  - new: https://git.openjdk.org/jdk/pull/29285/files/4f3d03a8..a561edc3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29285&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29285&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/29285.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29285/head:pull/29285

PR: https://git.openjdk.org/jdk/pull/29285