Canonicalize remove path

Say that my base folder for the mount points is `/home/mrshankly/mnt`.

Doing this wouldn't work:

```
$ cd /home/mrshankly
$ ldm -r mnt/<device_name>
```

You would have to give the full path `/home/mrshankly/mnt/<device_name>` for it to work.

The patch fixes this.