slapos_subscription_request: use source_project instead of follow_up

master/bt5/slapos_subscription_request/SkinTemplateItem/portal_skins/slapos_subscription_request/SubscriptionRequest_processRequest.py

@@ -32,7 +32,7 @@ request_kw.update(
     sla_xml=subscription_condition.getSlaXml(default_xml).strip(),
     shared=bool(subscription_condition.getRootSlave(0)),
     state="started",
-    project_reference=subscription_condition.getFollowUpReference()
+    project_reference=subscription_condition.getSourceProjectReference()
   )
 
 person.requestSoftwareInstance(**request_kw)