RFR 9: 8132735: java/lang/ProcessHandle/TreeTest failed with java.lang.AssertionError: Start with zero children

[Roger Riggs]

Please review this test fix so the test code only operates on processes 
it spawns.
On Windows, other processes may show up as children that are not part of 
the test.

Webrev:
  http://cr.openjdk.java.net/~rriggs/webrev-treetest-8132735/
Issue:
   https://bugs.openjdk.java.net/browse/JDK-8132735

Thanks, Roger