Update installer scripts for FreeNAS 12
As apart of the move into a pkg-base system for FreeNAS 12 (freenas/freenas-build repo), we'll need to update the installer script.
In particular the part where FreeNAS is extracted, will need to replaced with their pkg-base equivalents.
Here's some examples from TrueOS's pc-sysinstall program for reference:
On the installer image, there is a copy of the JSON manifest used for installation:
This is located at /var/db/trueos-manifest.json on the install media, and "jq" can be used to parse out the list of packages that need to be installed.