Impacted versions:
10.0 CE

Steps to reproduce:
Click on "button" "Compute from BOM" in product form view

Current behavior:

Raise an error with the following traceback:
```
Traceback (most recent call last):
  File "/home/manuel/Envs/odoo10/odoo/odoo/http.py", line 638, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/home/manuel/Envs/odoo10/odoo/odoo/http.py", line 675, in dispatch
    result = self._call_function(**self.params)
  File "/home/manuel/Envs/odoo10/odoo/odoo/http.py", line 331, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/home/manuel/Envs/odoo10/odoo/odoo/service/model.py", line 119, in wrapper
    return f(dbname, *args, **kwargs)
  File "/home/manuel/Envs/odoo10/odoo/odoo/http.py", line 324, in checked_call
    result = self.endpoint(*a, **kw)
  File "/home/manuel/Envs/odoo10/odoo/odoo/http.py", line 933, in __call__
    return self.method(*args, **kw)
  File "/home/manuel/Envs/odoo10/odoo/odoo/http.py", line 504, in response_wrap
    response = f(*args, **kw)
  File "/home/manuel/Envs/odoo10/odoo/addons/web/controllers/main.py", line 882, in call_button
    action = self._call_kw(model, method, args, {})
  File "/home/manuel/Envs/odoo10/odoo/addons/web/controllers/main.py", line 870, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/home/manuel/Envs/odoo10/odoo/odoo/api.py", line 681, in call_kw
    return call_kw_multi(method, model, args, kwargs)
  File "/home/manuel/Envs/odoo10/odoo/odoo/api.py", line 672, in call_kw_multi
    result = method(recs, *args, **kwargs)
  File "/home/manuel/Envs/odoo10/odoo/addons/product_extended/models/product.py", line 15, in compute_price
    return template.product_variant_id.compute_price()
  File "/home/manuel/Envs/odoo10/odoo/addons/product_extended/models/product.py", line 29, in compute_price
    price = product._calc_price(bom)
  File "/home/manuel/Envs/odoo10/odoo/addons/product_extended/models/product.py", line 47, in _calc_price
    total_cost += (order.time_cycle_manual/60) * order.workcenter_id.costs_hour
AttributeError: 'mrp.workcenter' object has no attribute 'costs_hour'
```
Expected behavior:
Standard Price Computed from BOM.

![screenshot-localhost 8083-2017-04-05-20-01-33](https://cloud.githubusercontent.com/assets/334317/24731816/83ba71a4-1a3a-11e7-9461-a5fbae4eefa4.png)

![fireshot capture 14 - pcsc234 computer sc234 - odoo_ - http___localhost_8083_web](https://cloud.githubusercontent.com/assets/334317/24731829/a26a3026-1a3a-11e7-8799-9996d1a49b86.png)

addons/product_extended/models/product.py
bom_obj = self.env['mrp.bom']
        action_rec = self.env.ref('stock_account.action_view_change_standard_price')
        for product in self:
            bom = bom_obj._bom_find(product=product)
            if bom:
                price = product._calc_price(bom)
                if action_rec:
                    action = action_rec.read([])[0]
                    action['context'] = {'default_new_price': price}
                    return action
        return True
    def _calc_price(self, bom):
        price = 0.0
        result, result2 = bom.explode(self, 1)
        for sbom, sbom_data in result2:
            if not sbom.attribute_value_ids:
                
                price += sbom.product_id.uom_id._compute_price(sbom.product_id.standard_price, sbom.product_uom_id) * sbom_data['qty']
        if bom.routing_id:
            total_cost = 0.0
            for order in bom.routing_id.operation_ids:
                total_cost += (order.time_cycle/60) * order.workcenter_id.costs_hour
            price += bom.product_uom_id._compute_price(total_cost, bom.product_id.uom_id)
        
        if price > 0:
            price = bom.product_uom_id._compute_price(price / bom.product_qty, self.uom_id)
        return price