Build recent ZFS on Scaleway / Dedibox rescue console

Summary:
Scaleway / Online still uses Ubuntu 20.04 (Focal Fossa) for rescue console.

ZFS is installed there, but it's an older version than FreeBSD current one.
That means we can't mount ZFS on rescue console.

This script automates the build of a fresh OpenZFS version,
we can run it at rescue console boot time to mount disks.

Ref T2110

Test Plan: Tested on Ubuntu 20.04.6 LTS (Focal Fossa)

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T2110

Differential Revision: https://devcentral.nasqueron.org/D3686