root-on-zfs /var/empty

I've seen a number of comments about the /var/empty dataset

The reason this is not set readonly=on during the installation is that
this causes the installation to fail (when the installer tries to
create/set flags).

This can be set during the post install, or it might be worth
considering Colin Percival's firstboot script as a way to set this after
the fact.


-- 
Allan Jude