Unbalance to unassigned disks

[cescm]

Would be possible to implement unbalance from array to unassigned disks?

[jbrodriguez]

If I recall correctly, I took a stab at supporting unassigned disks but found that some core code required quite some refactoring.

And since real world work has limited the time I can dedicate to other projects, I've had no option but leave this in the back log :)