title: Inherit model doesn't override field definition in Odoo 10
body: <p>I've created a module in Odoo 10 with the following code to inherit the <code>product.product</code> model and override the existing <code>standard_price</code> field definition to set it as a compute field:</p>
  
  <pre><code>class ProductProduct(models.Model):
      _inherit = 'product.product'
  
      standard_price = fields.Float(
          'Cost', company_dependent=True,
          digits=dp.get_precision('Product Price'),
          groups="base.group_user",
          compute='_compute_set_standard_price')
  
      def _compute_set_standard_price(self):
          .....
          # calculation for the value
          .....
          self.standard_price = 121 #this value is an example
  </code></pre>
  
  <p>The <code>standard_price</code> would be set to 121 because I've override the field definition to a compute field but the <code>standard_price</code> field is set to 0 and don't trigger the compute method. This code in Odoo v8 works fine.</p>
  
  <p>What's the way to override an existing field difinition in a inherited model?</p>