RFR 9: 8146012: CleanerTest fails: Cleanable should have been freed

[Roger Riggs]

Please review improvements to the CleanerTest to improve the reliability 
of the test.

Webrev:
  http://cr.openjdk.java.net/~rriggs/webrev-cleanertest-8146012/
Issue:
   https://bugs.openjdk.java.net/browse/JDK-8146012

Thanks, Roger