The ability to upgrade from legacy versions of FreeNAS (9.2 or earlier) should be removed. The suggested upgrade path has long been to upgrade to each consecutive major release. This upgrade process will have repartitioned the legacy disk format to create the new ZFS-based system, so it is time we shed the extra complexity to old-style upgrades from the install script.
When importing the freenas-boot pool to check a disk for a an existing FreeNAS install, the pool should be imported by its GUID instead of by name in case there are multiple pools with the name "freenas-boot". Likewise, use the GUID when importing the pool to create a boot-environment during in-place upgrades.