[FIX] product,float_utils: perform ceiling via float_round with new rounding_method UP

Modified product ceiling() to use float_round() with special mode
for rounding UP (away from zero), avoiding pathological cases where
float representations errors were ceiling to the superior unit.

Also added correspding tests for rounding_method=UP

Fixes issue #1125, and replaces PR #1126.
[FIX] product: _compute_qty: first round before ceiling, to avoid pathological cases

Fixes problem when we try to sell 12 units of a product and change it to 1 dozen,
the algorithm was then trying to recompute the original amount and was getting
12,0000048 as a result which was then passed to the ceiling method, getting 13.0!

See also previous commit and issue #1125, PR #1126