[FIX] website_sale: "Ship to the same address"

- Create a partner with an invoicing and a delivery address.
- Connect to the website as this partner, create an order
- In the "Shipping & Billing" page, the delivery address is selected
  automatically. Change and set to "Ship to the same address", and
  confirm.

The "Ship To" address is still the delivery address, while it should be
the same than the "Bill To" address.

This reintroduces the v8 behavior:
`order_info.update(partner_shipping_id=checkout.get('shipping_id') or partner_id)`
https://github.com/odoo/odoo/blob/8.0/addons/website_sale/controllers/main.py#L623

addons/website_sale/controllers/main.py

@@ -640,11 +640,10 @@ class website_sale(http.Controller):
                 shipping_info['lang'] = partner_lang
             shipping_info['parent_id'] = partner_id
             checkout['shipping_id'] = orm_partner.create(cr, SUPERUSER_ID, shipping_info, context)
-        if checkout.get('shipping_id'):
-            order.write({'partner_shipping_id': checkout['shipping_id']})
 
         order_info = {
             'message_partner_ids': [(4, partner_id), (3, request.website.partner_id.id)],
+            'partner_shipping_id': checkout.get('shipping_id') or partner_id,
         }
         order_obj.write(cr, SUPERUSER_ID, [order.id], order_info, context=context)