RFR 8035668: [test] Check that jstat does not cause problems when monitored application exits before jstat finishes its work

[Jaroslav Bachorik]

Please, review the addition of the jstat related test.

Issue : https://bugs.openjdk.java.net/browse/JDK-8035668
Webrev: http://cr.openjdk.java.net/~jbachorik/8035668/webrev.00/

The test logic is simple - first the application to be monitored is 
started. When the application is ready jstat is launched - it 
periodically (each 100ms) polls the monitored application status. At 
this moment the monitored application is signalled the possibility to 
exit - it waits for 500ms and exits. There should not be any errors 
neither in the monitored application nor jstat (checked by the exit 
status of their processes) and they should not hang (detected by the 
harness timeout).

Thanks,

-JB-