RFR(S/T) : 8219158 : use 'test.root' property instead of traversing test-src path

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev//8219158/webrev.00/index.html
> 73 lines changed: 9 ins; 32 del; 32 mod;

Hi all,

could you please review this trivial clean-up? jtreg4.2-b14 added a new property 'test.root', this patches replaces all code in hotspot testbase which determines the root directory w/ simple reading of this property.

JBS: https://bugs.openjdk.java.net/browse/JDK-8219158
webrev: http://cr.openjdk.java.net/~iignatyev//8219158/webrev.00/index.html
testing: vmTestbase/gc/g1/unloading, vmTestbase/nsk/monitoring/stress, vmTestbase/vm/mlvm/, vmTestbase/vm/runtime/defmeth

Thanks,
-- Igor