[jdk11u-dev] RFR: 8217825: Verify @AfterTest is used correctly in WebSocket tests

[Aleksey Shipilev]

Backporting to stabilize the tests and for `11.0.13-oracle` parity. Affected tests still pass.

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Commit messages:
 - Backport 11d43732bcabb6b4804bb64eb055e25f05b5c88f

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/116/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=116&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8217825
  Stats: 1240 lines in 4 files changed: 442 ins; 386 del; 412 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/116.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/116/head:pull/116

PR: https://git.openjdk.java.net/jdk11u-dev/pull/116