Some programs like eog seem to need dconf accessible on dbus.
Without this change I get

(eog:1738): dconf-WARNING **: 21:20:52.770: failed to commit changes to
dconf: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name
ca.desrt.dconf was not provided by any .service files

cc @lethalman @jtojnar as maintainers.
If this seem sensible to you, could you backport this to 18.09 ?

Things done

tested on nixos 18.09 beta, with xfce+i3.

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests) tested tests.gnome3 and tests.xfce.
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.