Create filesystem hierarchy for new boot environments based
on specifications in fhs.py file in truenas_install directory.
Exact spec for datasets is something we will fine-time as time
goes on.
This gives us more flexibility regarding which parts of FS to
make readonly, and also identifying precise local changes from
a pristine environment that users have made to system files.
Precise settings detailed in comments in the specification file.
Overall, this gives better posture for STIG compliance regarding
auditability and prevention of unauthorized OS changes.
