[jdk25u] RFR: 8361897: gc/z/TestUncommit.java fails with Uncommitted too slow

[Jayashree S Kumar]

A clean backport for [JDK-8361897](https://bugs.openjdk.org/browse/JDK-8361897)

This patch is loosens the threshold for flagging slow un-committing as an error in TestUncommit.java.

Backporting this patch can help fix intermittent issue in environments where external factors affect whether un-committing is run as expected. But ensure to still capture if the un-commit logic breaks completely.

Testing: Ran TestUncommit.java test (with and without JVM options) on all supported platforms and see them pass.

-------------

Commit messages:
 - Backport 3f21c8bd1f0cd7f27df940505b249ba7798940cf

Changes: https://git.openjdk.org/jdk25u/pull/233/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u&pr=233&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8361897
  Stats: 9 lines in 1 file changed: 9 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk25u/pull/233.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u.git pull/233/head:pull/233

PR: https://git.openjdk.org/jdk25u/pull/233