[FIXED JENKINS-24020] Fail-fast Matrix builds, as soon some configuration fail

I'll provide the Javadoc, but the method name, i don't think getResult to be expressive about the method purpose. It actually check for the job completion and if it's completed it notifies the completion before returning. (Not a good design, but just keeping some of the old behaviour).
We could agree about another (best) name for this, if needed.