Don't kill port-forwarding on the scale pod after build is done

Change-Id: Id80746cbf0178220acb3360158797fd26ff74d8b
diff --git a/jjb/pipeline/voltha-scale-test.groovy b/jjb/pipeline/voltha-scale-test.groovy
index 52e6246..4e33642 100644
--- a/jjb/pipeline/voltha-scale-test.groovy
+++ b/jjb/pipeline/voltha-scale-test.groovy
@@ -24,6 +24,7 @@
       timeout(time: 30, unit: 'MINUTES')
   }
   environment {
+    JENKINS_NODE_COOKIE=dontKillMe // do not kill processes after the build is done
     KUBECONFIG="$HOME/.kube/config"
     VOLTCONFIG="$HOME/.volt/config"
     SSHPASS="karaf"