Adding Default Parameter fix for JavaSampler

Hi

I have been working on an issue with the Java Sampler where the default
values keep on over-writing the configured values, and I couldn't add any
additional parameters into a test suite.

My colleague found this bug from 2007 and fix from 2013:

https://issues.apache.org/bugzilla/show_bug.cgi?id=42867

Any chance this patch could get applied into trunk for the next release?

Cheers

Peter