RFR: CODETOOLS-7903476: JMH: Threading model should not assume stable threads [v6]

[Aleksey Shipilev]

> See the bug for the original bug report.
> 
> This PR makes sure the harness code is able to work with different styles of executors, including the custom executor that always gives us a new thread. Integration tests now run with several important executor modes to catch errors early.

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

  More touchups

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Changes:
  - all: https://git.openjdk.org/jmh/pull/107/files
  - new: https://git.openjdk.org/jmh/pull/107/files/bcba7a3f..4b971d34

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jmh&pr=107&range=05
 - incr: https://webrevs.openjdk.org/?repo=jmh&pr=107&range=04-05

  Stats: 60 lines in 3 files changed: 21 ins; 0 del; 39 mod
  Patch: https://git.openjdk.org/jmh/pull/107.diff
  Fetch: git fetch https://git.openjdk.org/jmh.git pull/107/head:pull/107

PR: https://git.openjdk.org/jmh/pull/107