Create ZFS datasets for /var/home-wwwroot

Summary:
UNIX server convention is to serve on HTTP /~<username>
from /home/<username>/public_html directories.

On the devserver role, to allow to use chmod 700 in /home, nginx is configured
to serve user directories from the /var/home-wwwroot directory.

That creates a difference:

• home directories are ZFS datasets, with automatic snapshots
• web directories were regular all in the arcology/var ZFS dataset

This change creates arcology/var/home-wwwroot/<username> datasets with the same
permissions than user directories. Users can so create and manage snapshots.

The automatic provisionning of public_html in /home allows also to directly
use the public_html folder, without any root configuration.

This is a follow-up for e85e5bbf14ee.

Test Plan: Deployed on WindRiver

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D3473