RFR: 8307091: A few client tests intermittently throw ConcurrentModificationException [v2]

[Tejesh R]

> Few test are throwing Concurrent Modification Exception Intermittently. Since the issue is intermittent and from the log and code review, It is found that the shared variable `fileCache` is used in comparison with the `newFileCache` where the comparison invokes the iterator method in AbstractList class. Since based on vector documentation it was evident that listIterator are fail-fast iterators and hence it would be better to make a separate local copy of vectors for comparing operations. 
> The same is implemented and tested in CI system which shows green.

Tejesh R has updated the pull request incrementally with one additional commit since the last revision:

  Updated based on review comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13783/files
  - new: https://git.openjdk.org/jdk/pull/13783/files/5829aade..03493ba6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13783&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13783&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13783.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13783/head:pull/13783

PR: https://git.openjdk.org/jdk/pull/13783