Impacted versions: 9.0

Steps to reproduce:

* Create an MTO product with 
  * Product Type: Stockable Product
  * Routes: "Buy" and "Make to Order"
* Update Qty on Hand to any quantity (i.e, 2).
* Create a sales order with this product and a number <= to the one in the step before.
* Confirm the sales order.

Current behavior:

The created delivery picking appears in state "Reserved" and the current quantity on stock has been reserved, allowing you to transfer that stock.

Expected behavior:

The created delivery picking should be in "Waiting another operation", or at least in "Waiting availability" until the purchase order is confirmed (if you have defined a supplier for the product and the procurement creates the purchase order), which seems to be the current behavior when there's no stock available (is this also correct, as it allows to manually reserve?).
for packlot in self.browse(cr, uid, ids, context=context):
            if not packlot.lot_name and not packlot.lot_id:
                return False
        return True
    _constraints = [
        (_check_lot,
            'Lot is required',
            ['lot_id', 'lot_name']),
    ]
    _sql_constraints = [
        ('qty', 'CHECK(qty >= 0.0)','Quantity must be greater than or equal to 0.0!'),
        ('uniq_lot_id', 'unique(operation_id, lot_id)', 'You have already mentioned this lot in another line'),
        ('uniq_lot_name', 'unique(operation_id, lot_name)', 'You have already mentioned this lot name in another line')]
    def do_plus(self, cr, uid, ids, context=None):
        pack_obj = self.pool['stock.pack.operation']
        for packlot in self.browse(cr, uid, ids, context=context):
            self.write(cr, uid, [packlot.id], {'qty': packlot.qty + 1}, context=context)
        pack = self.browse(cr, uid, ids[0], context=context).operation_id
        qty_done = sum([x.qty for x in pack.pack_lot_ids])
        pack_obj.write(cr, uid, [pack.id], {'qty_done': qty_done}, context=context)
        return pack_obj.split_lot(cr, uid, [pack.id], context=context)
    def do_minus(self, cr, uid, ids, context=None):
        pack_obj = self.pool['stock.pack.operation']
        for packlot in self.browse(cr, uid, ids, context=context):
            self.write(cr, uid, [packlot.id], {'qty': packlot.qty - 1}, context=context)
        pack = self.browse(cr, uid, ids[0], context=context).operation_id
        qty_done = sum([x.qty for x in pack.pack_lot_ids])
        pack_obj.write(cr, uid, [pack.id], {'qty_done': qty_done}, context=context)
        return pack_obj.split_lot(cr, uid, [pack.id], context=context)
class stock_move_operation_link(osv.osv):