[jdk11u-dev] RFR: 8223716: sun/net/www/http/HttpClient/MultiThreadTest.java should be more resilient to unexpected traffic

[Goetz Lindenmaier]

I backport this as prerequisite of 8223783.

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Commit messages:
 - Backport e0a87ef8fcf35df77c3a4578723611cab32db07d

Changes: https://git.openjdk.org/jdk11u-dev/pull/1714/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1714&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8223716
  Stats: 47 lines in 1 file changed: 35 ins; 3 del; 9 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1714.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1714/head:pull/1714

PR: https://git.openjdk.org/jdk11u-dev/pull/1714