RFR 8071641: java/lang/management/ThreadMXBean/SynchronizationStatistics.java intermittently failed with NPE

[Jaroslav Bachorik]

Please, review the following test change.

Issue : https://bugs.openjdk.java.net/browse/JDK-8071641
Webrev: http://cr.openjdk.java.net/~jbachorik/8071641/webrev.00/

The test fails very intermittently with NPE. This seems to be caused by 
a data race between Thread.getStatus() and ThreadMXBean.getThreadInfo() 
- thread state is reported as BLOCKED but the ThreadInfo still contains 
a stale information (lockname == null).

The solution would be re-retrieving the ThreadInfo until it reflects the 
actual thread state.

-JB-