Allow replacing an active format within blivet's model.
Allow replacing an active format within blivet's model.

There is no reason to disallow this that I can think of as
we can tear things down right before we commit the changes.

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