Handle inactive RAID and crypto devices properly
Issue #2 (closed) dealt with the fact that there can be removable devices with unused swap space. unplug-me no longer complains about these.
However, the same problem still exists for inactive RAID and crypto devices, so we should handle them, too. In a later step we can also try to deactivate busy RAID and crypto devices. Yet, for the first step it should be enough to just detect unused RAID and crypto devices, so that we no longer consider them to be busy.