toccfs - relative base path while mounting

If toccfs is mounted with the relative base path, mounts without issue but operations such as ls gives following error.

```
# mount ./tocc-base-dir /mnt
# ls

ls: cannot access /mnt: Software caused connection abort
ls: cannot access /mnt: Transport endpoint is not connected
```

Expected Resolution:
- Convert to absolute path before mounting
- Or, error and exit
