[7u14] Request for approval for CR 8007142 - Add utility classes for writing better multiprocess tests in jtreg

[Yekaterina Kantserova]

Bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8007142
Webrev: http://cr.openjdk.java.net/~ykantser/8007142/webrev.02
Reviewed-by: alanb, rbackman
Pushed in jdk8: http://hg.openjdk.java.net/jdk8/tl/jdk/rev/2de8c6c2d652