RFR: 8027209: javax/management/monitor/ThreadPoolAccTest.java fails intermittently

[Erik Gahlin]

Could I have a review of this intermittently failing test.

Instead of doing Thread.sleep(2000) and assume principal is visible/set 
the test now spins until principal is available. I also cleaned up code 
to avoid warnings.

Thanks
Erik

Webrev:
http://cr.openjdk.java.net/~egahlin/8027209_3/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8027209