CHANGED: added resources for WarningsPluginTest; added test cases for Wa...

WarningsPluginTest + test resources
Sinnvoller wäre hier der Ansatz aus der Klasse https://github.com/jenkinsci/acceptance-test-harness/blob/master/src/main/java/org/jenkinsci/test/acceptance/plugins/AbstractCodeStylePluginPostBuildStep.java zu übernehmen.