ceph-volume: report slave devices in inventory

ceph-volume: report slave devices in inventory

`ceph-volume inventory` currently reports the following:

```

Device Path               Size        rotates available Model name
/dev/mapper/mpatha        50.00 GB    True    True
/dev/mapper/mpathaa       6.00 GB     True    True
/dev/mapper/mpathab       6.00 GB     True    True
/dev/mapper/mpathac       6.00 GB     True    True
/dev/mapper/mpathad       6.00 GB     True    True
/dev/mapper/mpathae       6.00 GB     True    True
```

whereas something like following would be useful:

```

Device Path               Size         Device nodes    rotates available Model name
/dev/mapper/mpatha        50.00 GB     sdf,sde         True    True
/dev/mapper/mpathaa       6.00 GB      sdbe,sdat       True    True
/dev/mapper/mpathab       6.00 GB      sdav,sdbf       True    True
/dev/mapper/mpathac       6.00 GB      sdbb,sdbl       True    True
/dev/mapper/mpathad       6.00 GB      sdas,sdbc       True    True
/dev/mapper/mpathae       6.00 GB      sdax,sdbh       True    True
```

Fixes: https://tracker.ceph.com/issues/56624
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>