RFR: 8323670: A few client tests intermittently throw ConcurrentModificationException

[Tejesh R]

Suggested fix [JDK-8307091](https://bugs.openjdk.org/browse/JDK-8307091) also created concurrent exception intermittently (monthly once/quarterly once) on CI system. The issue was not able to be reproduced yet, hence proposing an alternative fix which uses iterators to compare the List.
CI testing shows green.

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/17462/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17462&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323670
  Stats: 17 lines in 1 file changed: 13 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/17462.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17462/head:pull/17462

PR: https://git.openjdk.org/jdk/pull/17462