When I normally install systems I do not like to give the full disk
to the zroot partition. If only because I want to use the remainder
of the disk for pools of a different ZMIRRO/ZRAID type.
ATM this is only doable by first creating an absurde SWAP size.
And once booted fix that. Disadvantage is that the freespace ends
between swap and zroot, which is not all to nice.

This patch add a extra option in the zfsboot menu that allows to
deviate from the MAX setting. MAX setting gives the current
standard behaviour.