daemon: Use $XDG_RUNTIME_DIR to create keyring socket directory

We create a predictable location under $XDG_RUNTIME_DIR. GNOME does
not support multiple GUI sessions per user, so using a predictable
directory works well for us.

If someone somewhere still wants an alternate location use the
--control-directory argument.

https://bugzilla.gnome.org/show_bug.cgi?id=725801