Review request for a test fix for 6992968

[Mandy Chung]

  6992968: 
test/java/lang/management/MemoryMXBean/CollectionUsageThresholdConcMarkSweepGC.sh 
should not hang

Webrev at:
    http://cr.openjdk.java.net/~mchung/6992968/webrev.00/

If the test fails, the main thread is waiting for the checker thread to 
finish checking the result but the checker thread terminates with an 
exception.  The test hangs and the main thread is forever waiting for a 
monitor to be notified.  I update the test to use the new concurrent 
utility and reset a CyclicBarrier that causes a BrokenBarrierException 
to be thrown in the main thread.

I also add @ignore to CollectionUsageThresholdConcMarkSweepGC.sh test 
until 6982965 is fixed.

Mandy