source_panel: use souce_project to find the trade condition

no need to trick source/destination project anymore, as trade_condition_type is used

master/bt5/slapos_panel/SkinTemplateItem/portal_skins/slapos_panel/Person_addVirtualMaster.py

@@ -65,7 +65,7 @@ sale_trade_condition = portal.sale_trade_condition_module.newContent(
   reference=title,
   trade_condition_type="compute_node",
   specialise_value=specialise_value,
-  destination_project_value=project,
+  source_project_value=project,
   source_value=subscription_request.getSourceValue(),
   source_section_value=source_section_value,
   #source_payment_value=seller_bank_account,