Allow systemd-hostnamed to create socket when called from Varlink

Summary:
"snap, SELinux, systemd and a full Rust piece of software
to set a prompt are in a boat..."

Fixes T2113.

Test Plan: Deploy on Dwellers

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T2113

Differential Revision: https://devcentral.nasqueron.org/D3658