RFR: 8364786: Test java/net/vthread/HttpALot.java intermittently fails - 24999 handled, expected 25000 [v3]

[Jaikiran Pai]

> Can I please get a review of this test-only change which proposes to fix an intermittent failure in that test? This addresses https://bugs.openjdk.org/browse/JDK-8364786.
> 
> As noted in that issue, the test fails because the main thread doesn't wait for the server side HttpHandler instances to return from the handle() method. There are 2 commits in this PR - one is general clean up and additional logging and the second one is the actual fix where we `close()` the server side `Executor` before asserting a counter state in the main thread. Closing the server side `Executor` waits till the HttpHandler instances return from their handle() method and thus prevents these intermittent test failures.
> 
> The reporter of the JBS issue has tested this proposed fix in their setup and the test no longer fails. I have also triggered a test repeat (and tier testing) for this change in our CI.

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

  Daniel's review - close the server Executor after server.stop()

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26686/files
  - new: https://git.openjdk.org/jdk/pull/26686/files/30044906..fd5298ca

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26686&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26686&range=01-02

  Stats: 13 lines in 1 file changed: 4 ins; 2 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/26686.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26686/head:pull/26686

PR: https://git.openjdk.org/jdk/pull/26686