RFR 8056143: interrupted java/lang/management/MemoryMXBean/LowMemoryTest.java leaves running process

[Jaroslav Bachorik]

Please, review the following test change

Issue : https://bugs.openjdk.java.net/browse/JDK-8056143
Webrev: http://cr.openjdk.java.net/~jbachorik/8056143/webrev.00

The method jdk.testlibrary.ProcessTools.getOutput(process) waits for the 
given process to finish (process.waitFor()) before grabbing its outputs. 
However, the code does not handle the process.waitFor() being 
interrupted correctly - it just goes ahead and tries to obtain the exit 
code which will fail and leave the tested process running.

The correct way is to forcibly destroy the process when 
process.waitFor() is interrupted or throws ExecutionException to make 
sure the process has actually exited before checking its exit code.

Thanks,

-JB-