8307091: A few client tests intermittently throw ConcurrentModificationException

[luchenlin]

Due to JDK-8327137 and JDK-8323670 depends on this, so i will backport this first, and then backport the others.

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Progress

• [x] Change must not contain extraneous whitespace
• [x] Commit message must refer to an issue
• [ ] JDK-8307091 needs maintainer approval

Issue

• JDK-8307091: A few client tests intermittently throw ConcurrentModificationException (Bug - P2)

Reviewing

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