Fixing JENKINS-24802

Corrected issue explained in https://issues.jenkins-ci.org/browse/JENKINS-24802
Refactored SubversionRepositoryStatus to make onNotify method shorter and more "understandable"
Added unit tests for one refactored method
Shouldn't inner tested class (JobTriggerListenerImpl) should have its corresponding inner test class (JobTriggerListenerImplTest) ?