Template test and some changes to the library to test triggerIfResult options of NLP plugin

This single test (trigger_if_succeeds_with_failed_build) shall be the template to test any combination of build results and triggerIfResult option of the node parameter. At the moment it fails for the last statement (job should not have built on the second slave).

The intention of this pull request is to discuss whether this approach is appropriate to test those options and was requested by oliver gondža. (That's also the reason why it is written in English)

With regards to the console output during the test, I assume that the triggerIfResult checks do only consider the main build action which is completed with SUCCESS whilst the overall build / job result is failed due to text-finder execution.

Another point to be discussed: I'm not really happy with the way BuildHistory's shouldInclude method works (return if found, NoSuchElementException if not) used by Job's shouldHaveBuiltOn method. However, I implemented a shouldHaveNotBuiltOn method which deals with this behavior but creates the necessity of an explicit fail() call.