[jdk11u-dev] RFR: 8307091: A few client tests intermittently throw ConcurrentModificationException

[Andrew Lu]

I backport this for parity with 11.0.24-oracle.

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Commit messages:
 - Backport 465bdd9e416cacc6cc7dd91a29cc84adf2eaf1ed

Changes: https://git.openjdk.org/jdk11u-dev/pull/2720/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2720&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307091
  Stats: 18 lines in 1 file changed: 8 ins; 2 del; 8 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2720.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2720/head:pull/2720

PR: https://git.openjdk.org/jdk11u-dev/pull/2720