nixos/nixos-containers: user options take precedence over module ones (#388409)

      exec ${config.systemd.package}/bin/systemd-nspawn \

        --keep-unit \

        -M "$INSTANCE" -D "$root" "''${extraFlags[@]}" \

        $EXTRA_NSPAWN_FLAGS \

        --notify-ready=yes \

        --kill-signal=SIGRTMIN+3 \

        --bind-ro=/nix/store:/nix/store$NIX_BIND_OPT \

        ${optionalString (cfg.tmpfs != null && cfg.tmpfs != [])

          ''--tmpfs=${concatStringsSep " --tmpfs=" cfg.tmpfs}''

        } \

        $EXTRA_NSPAWN_FLAGS \

        ${containerInit cfg} "''${SYSTEM_PATH:-/nix/var/nix/profiles/system}/init"

    '';