RFR 8239893: Windows handle Leak when starting processes using ProcessBuilder

[Roger Riggs]

Please review a change to the Windows ProcessImpl to ensure that the handles
created for the input and output streams of a process are closed when no 
longer referenced.

Unlike on Linux, there is no thread monitoring the process that can 
close the streams.
The FileDescriptors are registered with the Cleaner to be closed when 
they are no longer referenced.

A test is added that monitors the count of handles as 50 Processes are 
launched and exit.
The test and change only affect the Windows implementation.

Webrev:
   http://cr.openjdk.java.net/~rriggs/webrev-handles-8239893/

Issue:
   https://bugs.openjdk.java.net/browse/JDK-8239893

Thanks, Roger