Fixes issue with spaces in filesystem name.

In some cases a filesystem name returned by `/bin/df` can contain a space, which causes the original command to mix up the columns:
```
Filesystem                 Type     1K-blocks     Used Available Use% Mounted on
rootfs                     rootfs     7430700  3073596   4009880  44% /
//192.168.1.254/Disque dur cifs     239216096 80122196 146919316  36% /mnt/Freebox

```
In that case we can't rely on awk to separate columns with the space character. In this commit I basically removed the whole filesystem column since it is not used.