Fix for lvcreate vs. lvs case-sensitivity

lvcreate is case-*insenstive* with respect to units
i.e. 'g' = 'G' = GiB = powers of 2

lvs is case-*senstive* with respect to units
i.e. 'g' = powers of 10; 'G' = powers of 2

This causes the lvol module to want to shrink LV's if the size argument
is specified with an uppercase unit.

The fix is to always set the size unit to lower case.