RFR 8059034: ProcessTools.startProcess() might leak processes

[Jaroslav Bachorik]

Please, review the following change to the JDK test library class

Issue : https://bugs.openjdk.java.net/browse/JDK-8059034
Webrev: http://cr.openjdk.java.net/~jbachorik/8059034/webrev.00

Currently, the ProcessTools.startProcess() might leave a dangling 
process behind when a timeout or interrupt happens. The solution is to 
try and forcibly terminate the forked process when this happens.

Thanks,

-JB-