RFR(S): 8141353 - Testlibrary: add various changes into testlibrary Utils

[dmitrij pochepko]

Hi,

please review patch for enhancement JDK-8141353 - Testlibrary: add 
various changes into testlibrary Utils

A jdk.test.lib.Utils class is modified to read 'test.jdk' and 
'test.classes' system properties provided by jtreg.

Also, a small method to request any mandatory property for tests is added.

CR: https://bugs.openjdk.java.net/browse/JDK-8141353
Webrev: http://cr.openjdk.java.net/~dpochepk/8141353/webrev.01/

Thanks,
Dmitrij