We have a customer whose base unit for selling stuff is in thousands.  However stock can be as low as 0.001 thousands, but that last decimal place isn't displayed in the stock warning.

As you'll see from the example of "actual behaviour" below this is confusing.

Impacted versions:
- 8.0

Steps to reproduce:
- Install product and sale
- Create a unit of measure with:
  - Name: Thousand(s)
  - Product Category: Unit
  - Type: Bigger than the reference Unit of Measure
  - Bigger Ratio: 1000
  - Rounding Precision: 0.00100
- Create a product 'Widget' with
  - type = Stockable Product
  - UoM = Thousand(s)
- Create a Quotation
- Add to the Sales Order a line
- Choose Product: Widget
- Change Quantity to: 0.001 Thousand(s)

Current behavior:

Configuration Error!

```
Not enough stock ! : You plan to sell 0.00 Thousand(s) but you only have 0.00 Thousand(s) available !
The real stock is 0.00 Thousand(s). (without reservations)
```

Expected behavior:

Configuration Error!

```
Not enough stock ! : You plan to sell 0.001 Thousand(s) but you only have 0.000 Thousand(s) available !
The real stock is 0.000 Thousand(s). (without reservations)
```

addons/sale_stock/models/sale_order.py
if self.warehouse_id.company_id:
            self.company_id = self.warehouse_id.company_id.id
    @api.multi
    def action_view_delivery(self):
        '''
        This function returns an action that display existing delivery orders
        of given sales order ids. It can either be a in a list or in a form
        view, if there is only one delivery order to show.
        '''
        action = self.env.ref('stock.action_picking_tree_all').read()[0]
        pickings = self.mapped('picking_ids')
        if len(pickings) > 1:
            action['domain'] = [('id', 'in', pickings.ids)]
        elif pickings:
            action['views'] = [(self.env.ref('stock.view_picking_form').id, 'form')]
            action['res_id'] = pickings.id
        return action
    @api.multi
    def action_cancel(self):
        self.order_line.mapped('procurement_ids').cancel()
        return super(SaleOrder, self).action_cancel()
    @api.multi
    def _prepare_invoice(self):
        invoice_vals = super(SaleOrder, self)._prepare_invoice()
        invoice_vals['incoterms_id'] = self.incoterm.id or False
        return invoice_vals
    @api.model
    def _prepare_procurement_group(self):