daemon: btrfs: Upstream 'btrfs device add' command now needs '--force' option to work.

However earlier versions didn't have the --force option, so we
have to detect it.

(cherry picked from commit 59596810b009744316941da8ef18b7e75b503b9f)
(cherry picked from commit 899d0af8291baa1b714024fcdd684db10f4ae262)