RFR: JDK-8303742: CompletableFuture.orTimeout leaks if the future completes exceptionally

[Viktor Klang]

Improves the stability of the memory leak test for CompletableFuture timeout cancellation by both reducing the count by 50% (which should still be above threshold to trigger given the ample margin set initially) as well as extending the default timeout of the test run.

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Commit messages:
 - Hardening the memory leak test for CompletableFuture timeout cancellation

Changes: https://git.openjdk.org/jdk/pull/13116/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13116&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303742
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13116.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13116/head:pull/13116

PR: https://git.openjdk.org/jdk/pull/13116