cgroups: Allow percent values in cgroup.conf to be floating point

The use of whole percent values for cgroup.conf parameters such
as AllowedRAMSpace, MaxRAMPercent, AllowedSwapSpace and MaxSwapPercent
may be too coarse grained on systems with large amounts of memory.
(e.g. 1% of 64G is over 650MB).

This patch allows these percentage values to be arbitrary floating
point numbers to allow finer grained tuning of these limits and
parameters.