RFR 9: 8130296 [TESTBUG] java/lang/ProcessHandle/OnExitTest - Unaccounted for children

[Roger Riggs]

Please review this change to a ProcessHandle test to address intermittent failures. 
Unexpected subprocesses has been observed. The test succeeds if all of the 
processes under test are accounted for; others are ignored. 

Webrev: 
http://cr.openjdk.java.net/~rriggs/webrev-exit-8130296/ 

Issue: 
https://bugs.openjdk.java.net/browse/JDK-8130296 

Thanks, Roger