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.
Update installer script
This commit updates installer script to work with FN 12.