[UIMA-6457] Clean Jenkins workspace up after build

- Clean only on success
diff --git a/vars/defaultPipeline.groovy b/vars/defaultPipeline.groovy
index 8d77305..b5647b6 100644
--- a/vars/defaultPipeline.groovy
+++ b/vars/defaultPipeline.groovy
@@ -161,7 +161,7 @@
           }
           
           post {
-            always {
+            success {
               script {
                 if (params.wipeWorkspaceAfterBuild) {
                   echo "Wiping workspace..."