RFR: 8368821: Test java/net/httpclient/http3/GetHTTP3Test.java intermittently fails with java.io.IOException: QUIC endpoint closed

[Jaikiran Pai]

Can I please get a review of this test-only change which addresses intermittent failures in `GetHTTP3Test` and `PostHTTP3Test`?

As noted in https://bugs.openjdk.org/browse/JDK-8368821, these two tests have been reported to fail intermittently, especially when the host on which it runs is under heavy resource usage or when run with JVM options like `-Xcomp`.

The commit in this PR removes the connection timeout that was enforced on the connection attempts by the test. As far as I can see, they aren't necessary for what this test is testing. The change also updates a few other places in this test which had specific values for timeouts when checking if the `HttpClient` had shutdown. These places have been updated to take into account the timeout factor when computing the timeout.

The changes have been verified by Matthias and SendaoYan who originally reported these issues. I will run this change in our CI too before integrating.

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Commit messages:
 - 8368821: Test java/net/httpclient/http3/GetHTTP3Test.java intermittently fails with java.io.IOException: QUIC endpoint closed

Changes: https://git.openjdk.org/jdk/pull/27619/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27619&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368821
  Stats: 15 lines in 2 files changed: 4 ins; 4 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/27619.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27619/head:pull/27619

PR: https://git.openjdk.org/jdk/pull/27619