[9] RFR (XS) 8066508: JTReg tests timeout on slow devices when run using JPRT

[Chris Plummer]

Please review the following fix to address JPRT timeout issues when 
using -rtests to run hotspot JTReg tests on slow devices. The same logic 
has been in place for jdk/test/Makefile for a while now, so I just 
copied from there to hotspot/test/Makefile.

https://bugs.openjdk.java.net/browse/JDK-8066508
http://cr.openjdk.java.net/~cjplummer/8066508/webrev.00/
thanks,

Chris