[jdk8u-dev] RFR: 8048215: [TESTBUG] java/lang/management/ManagementFactory/ThreadMXBeanProxy.java Expected non-null LockInfo

[SendaoYan]

Hi all,
  This is clean backport of [JDK-8048215](https://bugs.openjdk.org/browse/JDK-8048215). This PR try to fixed the intermitent failure. The change has been verifed. Only change the testcase, no risk.

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Commit messages:
 - 8048215: [TESTBUG] java/lang/management/ManagementFactory/ThreadMXBeanProxy.java Expected non-null LockInfo

Changes: https://git.openjdk.org/jdk8u-dev/pull/504/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=504&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8048215
  Stats: 13 lines in 1 file changed: 7 ins; 1 del; 5 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/504.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/504/head:pull/504

PR: https://git.openjdk.org/jdk8u-dev/pull/504