Integrate ZFS modeler into ZPool modeler

[daviswr]

There is no order in which modelers are executed, so it's possible for the ZFS modeler to run prior to the ZPool modeler the first time a system is modeled, this missing the datasets due to ZPool components not yet having been created.

Probably can't stub-out Pools in case ZFS runs after ZPool, which would replace the previously-made components (I think...)

Subsequent models are normally fine.