mrp: it was bad idea to set transformation on line if several transformations are found

Some tests where explicitely checking that transformation is not set in case
several are found. It is indeed better to ask user decision in such case.

bt5/erp5_mrp/WorkflowTemplateItem/portal_workflow/production_order_interaction_workflow/scripts/ProductionOrderLine_setTransformationFromResource.py

@@ -11,6 +11,6 @@ if transformation is None:
       portal_type=portal.getPortalTransformationTypeList(),
       validation_state="!=invalidated",
       default_resource_uid=resource_uid)
-    if len(transformation_list) >= 1:
+    if len(transformation_list) == 1:
       transformation = transformation_list[0].getRelativeUrl()
       production_order_line.setSpecialise(transformation)