[FIX] mrp: do not reset back stock moves to confirm

For instance, setting a BOM Phantom with:
Finished product: stockable, MTO Manufacture
Components: stockable, MTS, Buy. Inventory set to 1000
Stock moves of components are directly set to assigned once the procurement confirmed thanks to JIT
The stock moves should not be set back to confirmed after they have been assigned
Merge branch '7.0' of https://github.com/odoo/odoo into 7.0-win32