RFR 9: 8086208 : java/lang/ProcessHandle/OnExitTest.java: IllegalThreadStateException: process hasn't exited

[Roger Riggs]

Please review a fix for a (Unix) race condition for the exit status of 
Process.onExit.
And some source cleanup of OnExitTest.

Webrev:
    http://cr.openjdk.java.net/~rriggs/webrev-race-8086208/

Issue:
    https://bugs.openjdk.java.net/browse/JDK-8086208

Roger