RFR: 8028583 :Add helper methods to test libraries

[Seán Coffey]

Looking to add two helper methods to the OpenJDK test libraries. I'm 
looking to clean up a closed src test case but these methods should be 
of use for future testcase development.

webrev : http://cr.openjdk.java.net/~coffeys/webrev.8028583/webrev/
bug report : https://bugs.openjdk.java.net/browse/JDK-8028583
regards,
Sean.