Issue description

I'd like to be able to set my timezone using timedatectl, as I'm not always in the same timezone with my laptop and don't think its configuration should have to reflect my current location. NixOS/systemd@f65b136 hardcodes prevention of setting the time zone via this mechanism (and also causes #14877). It would be nice to refine this code to allow setting time and timezone via timedatectl.

In fact, I'm not sure the timezone should live in the NixOS config at all. Any thoughts on that?

Steps to reproduce

timedatectl set-timezone Europe/London

Technical details

• System: 17.03.1264.9ed5dbafe3 (Gorilla)
• Nix version: nix-env (Nix) 1.11.8
• Nixpkgs version: "17.03.1264.9ed5dbafe3"
• Sandboxing enabled: true