[FIX] stock: scrap and sublocations

Following the previous commit, it appears than the scrap mechanism needs
some rigorousness when looking for quants characteristics (i.e. if we
look for a quant without `lot_id`, it should not return one with one)
but some flexibility with the location (i.e. we can look in sublocations
to find one with the given characteristics).

Before this commit, we centralized everything related to quant's search
in stock_quant.py and the `_gather` method, which has a `strict` kw. As
we exposed the `_get_quantity` method but is only used in stock_scrap,
and that the `strict` flag does not fulfill the needs of stock_scrap, we
inline the appropriate search, as it was done previously.

addons/stock/models/stock_quant.py

@@ -102,12 +102,6 @@ class StockQuant(models.Model):
 
         return self.search(domain, order=removal_strategy_order)
 
-    @api.model
-    def _get_quantity(self, product_id, location_id, lot_id=None, package_id=None, owner_id=None, strict=False):
-        self = self.sudo()
-        quants = self._gather(product_id, location_id, lot_id=lot_id, package_id=package_id, owner_id=owner_id, strict=strict)
-        return sum(quants.mapped('quantity'))
-
     @api.model
     def _get_available_quantity(self, product_id, location_id, lot_id=None, package_id=None, owner_id=None, strict=False):
         """ Return the available quantity, i.e. the sum of `quantity` minus the sum of

addons/stock/models/stock_scrap.py

@@ -80,10 +80,13 @@ class StockScrap(models.Model):
         for scrap in self:
             move = self.env['stock.move'].create(scrap._prepare_move_values())
             if self.product_id.type == 'product':
-                quantity_in_stock = self.env['stock.quant']._get_quantity(
-                    self.product_id, self.location_id, lot_id=self.lot_id,
-                    package_id=self.package_id, owner_id=self.owner_id, strict=True
-                )
+                quantity_in_stock = sum(self.env['stock.quant'].search([
+                    ('product_id', '=', self.product_id.id),
+                    ('lot_id', '=', self.lot_id and self.lot_id.id or False),
+                    ('package_id', '=', self.package_id and self.package_id.id or False),
+                    ('owner_id', '=', self.owner_id and self.owner_id.id or False),
+                    ('location_id', 'child_of', self.location_id.id)
+                ]).mapped('quantity'))
                 if quantity_in_stock < move.product_qty:  # FIXME: float compare
                     raise UserError(_('You cannot scrap a move without having available stock for %s. You can correct it with an inventory adjustment.') % move.product_id.name)
             move.action_done()