[FIX] purchase: select supplier

When a PO is created through the resolution of a procurement, the first
supplier of the list is automatically chosen. This is hardcoded and
cannot be extended.

We add a hook so it's possible to customize the selection of the
supplier, for example by selecting the one who offers the best price.

opw-726309

addons/purchase/models/purchase.py

@@ -976,6 +976,12 @@ class ProcurementOrder(models.Model):
             'group_id': group
         }
 
+    def _make_po_select_supplier(self, suppliers):
+        """ Method intended to be overridden by customized modules to implement any logic in the
+            selection of supplier.
+        """
+        return suppliers[0]
+
     @api.multi
     def make_po(self):
         cache = {}
@@ -985,7 +991,7 @@ class ProcurementOrder(models.Model):
             if not suppliers:
                 procurement.message_post(body=_('No vendor associated to product %s. Please set one to fix this procurement.') % (procurement.product_id.name))
                 continue
-            supplier = suppliers[0]
+            supplier = self._make_po_select_supplier(suppliers)
             partner = supplier.name
 
             gpo = procurement.rule_id.group_propagation_option