Test test test

Hoping it will help plugins to mature out of experimental/beta so they will be aligned with logstash inner-peace stability and good quality :smiley_cat: 

I needed to make minor adjustment to test_util to give the same block as in filterworker to be yield by split/clone filters + saner handling of multiple vs single results

Also foundAndFix one bug raised by the last filter/clone test, event#clone methods was not a *deep-ish* copy as the comment stated, so I fixed it in event_v0 following the advice from here
http://boonedocks.net/mike/archives/188-Rubys-shallow-copies-of-hashes.html
if you agree, please update event_v1 too.