RFR: 8372704: ThreadMXBean.getThreadUserTime may return total time

[Jonas Norlinder]

getThreadUserTime will return total (system + user) time if called with e.g. ManagementFactory.getThreadMXBean().getThreadUserTime(Thread.currentThread().threadId()).

The specification for this methods states that only user-level CPU time would ever be returned on success.

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Commit messages:
 - Remove debug pritn
 - Revert to old behaviour

Changes: https://git.openjdk.org/jdk/pull/28545/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28545&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372704
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28545.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28545/head:pull/28545

PR: https://git.openjdk.org/jdk/pull/28545