[FIX] product: when converting unit of mesures, round above instead of mathematical rounding
[IMP] mrp: use also the ceiling method from product
[IMP] product: add python tests
[IMP] remove useless imports
[FIX] product: when converting unit of mesures, use ceiling instead of rounding method

This avoids flows to be stucked when a convertion would move/reserve/buy less pieces than the number required (eg: MTO product where supplier has a UoM bigger than the one on the sale order)
[FIX] use float rounding for pricelist instead of ceiling
[FIX] use float rounding for pricelist instead of ceiling