When a btrfs subvol's name is changed, change its subvol argument too.
When a btrfs subvol's name is changed, change its subvol argument too.

Related: rhbz#892363

dwlehman/blivet,jkonecny12/blivet,dwlehman/blivet,rhinstaller/blivet,vojtechtrefny/blivet,rhinstaller/blivet,jkonecny12/blivet,vojtechtrefny/blivet,AdamWill/blivet,vpodzime/blivet,rvykydal/blivet,rvykydal/blivet,AdamWill/blivet,vpodzime/blivet