Adding redback build as upstream trigger

Jenkinsfile

@@ -46,6 +46,10 @@ pipeline {
     agent {
         label "${LABEL}"
     }
+    // Build should also start, if redback has been built successfully
+    triggers { 
+        upstream(upstreamProjects: 'Archiva-TLP-Gitbox/archiva-redback-core/master', threshold: hudson.model.Result.SUCCESS) 
+    }
     options {
         disableConcurrentBuilds()
         buildDiscarder(logRotator(numToKeepStr: '7', artifactNumToKeepStr: '5'))