Sourcing the release file before setting custom EXTRA_HELM_PARAMS in the scale job

Change-Id: I359cff76ff1bc444acf9a4c5f46d91e340513344
diff --git a/jjb/voltha-scale.yaml b/jjb/voltha-scale.yaml
index 816b41a..a55d91f 100644
--- a/jjb/voltha-scale.yaml
+++ b/jjb/voltha-scale.yaml
@@ -428,7 +428,7 @@
       - string:
           name: extraHelmFlags
           default: '{extraHelmFlags}'
-          description: 'Any extra helm parameters you want (passed to every helm install command)'
+          description: 'Any extra helm parameters you want (passed to every helm install command, not available if release != master)'
 
       - string:
           name: openonuAdapterReplicas