RFR (XS): Run SPECjbb in headless mode in JPRT

[Mikael Vidstedt]

All,

I'd like to get a couple of reviews of this change.

We've seen problems with intermittent and hard to debug popups when 
running SPECjbb on lights out OSX machines. To prevent the popups from 
blocking the completion of the tests this change makes SPECjbb run in 
headless mode in JPRT.

http://cr.openjdk.java.net/~mikael/7155453/webrev.00

Thanks,
Mikael