Percentage Free Random Distribution
Chooses a random branch based on the available space percentage free.
IE: if branch A has 1G free and branch B has 2G then B should be chosen
twice as often.
Just like functions you can now set a policy for moveonfreenospc. This
allows for more flexibility.
For backwards compatibility moveonfreenospc=true is converted to
moveonfreenospc=mfs.
minfreespace does apply which is slightly different from original behavior.