RFR 8034168: ThreadMXBean/Locks.java failed, blocked on wrong object

[Jaroslav Bachorik]

Please, review the following test change.

Issue : https://bugs.openjdk.java.net/browse/JDK-8034168
Webrev: http://cr.openjdk.java.net/~jbachorik/8034168/webrev.00

The test fails because of falsely evaluating the thread being parked as 
actually waiting on a monitor. This is because there is no difference in 
java thread state for those two situations. The test is using Phaser for 
synchronization between the checked and checking thread to make sure an 
appropriate code section is entered before performing asserts. Then it 
checks the checked thread state and waits till it becomes WAITING. 
Unfortunately, when Phaser needs to wait it parks the thread and sets 
the thread state to WAITING. From now on the test is in a completely 
random state and the result will largely depend on timing - thus failing 
intermittently.

The solution is to use an additional volatile variable to prevent 
falsely indicating the park() induced WAITING state.

Thanks,

-JB-