RFR 9: 8086278 : java/lang/ProcessHandle/TreeTest.java failed - ProcessReaper StackOverflowException

[Roger Riggs]

Please review an increase in the default stack size of the Process 
reaper thread to 48K from 32k.
Some tests with various VM arguments are failing intermittently.
The failures are not reproducible.

Webrev:
    http://cr.openjdk.java.net/~rriggs/webrev-reaper-stack-8086278/

Issue:
    https://bugs.openjdk.java.net/browse/JDK-8086278

Thanks, Roger