8006413: Add utility classes for writing better multiprocess tests in jtreg

[Yekaterina Kantserova]

Hi everyone,

Christian Törnqvist has done a great job to make it easier to run 
multi-process tests in jtreg. His webrev 
(http://cr.openjdk.java.net/~ctornqvi/webrev/8006413/webrev.03/) is 
already approved and on the way into the hotspot repo.

This webrev http://cr.openjdk.java.net/~ykantser/8006413/webrev.00/ is 
for putting these utility classes into the jdk repo. I'm going to use 
them for the JFR testing in the first hand.

The webrev is almost a copy of Christian's except JcmdBase.java, utility 
class for starting jcmd, and some extra methods in OutputAnalyzer.java.

Thanks,
Katja