NUnitPublisher no longer respects failIfNoResults

Since the implementation of SimpleBuildStep, the boolean returning implementation of "perform" is no longer called, and the void returning version does nothing when NUnitArchiver returns false.

See https://github.com/jenkinsci/nunit-plugin/blob/master/src/main/java/hudson/plugins/nunit/NUnitPublisher.java, lines 141 and 275.