RFR: 8269478: Shenandoah: gc/shenandoah/mxbeans tests should be more resilient [v5]

[Aleksey Shipilev]

> After JDK-8259954, some mxbeans tests wait in the effectively infinite loop for the notifications to arrive. If notifications are broken, it would wait forever, and test would timeout. We need to make such failure mode more straightforward.
> 
> Additional testing: 
>  - [x] Linux x86_64 fastdebug `gc/shenandoah/mxbeans` 
>  - [x] Linux x86_64 fastdebug `gc/shenandoah/mxbeans`, `-Xcomp`

Aleksey Shipilev 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 one additional commit since the last revision:

  8269478: Shenandoah: gc/shenandoah/mxbeans tests should be more resilient

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4611/files
  - new: https://git.openjdk.java.net/jdk/pull/4611/files/a9eeaeff..612957fd

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4611&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4611&range=03-04

  Stats: 3465 lines in 70 files changed: 1891 ins; 1193 del; 381 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4611.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4611/head:pull/4611

PR: https://git.openjdk.java.net/jdk/pull/4611