Fix: rework utils_parse_size_suffix

Ok, so there are a lot of problems with this function (sorry :|). Taking
the regex road is probably to complicated for nothing, so here is a
version without regexes.

I added many test cases as suggested by Sandeep Chaudhary and Daniel
Thibault. I tested on both Intel 32 and 64 bits.

Fixes #633

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Signed-off-by: David Goulet <dgoulet@efficios.com>