Ensure we recognize (and avoid) raid devices

[nettings]

I'm pretty sure the current heuristics would miss that the two first disks in this example (my dev box) are part of a raid, because the sdX1 partition has no mountpoint. Instead there is an additional raid device below, which doesn't share a common prefix with the disk device and thus wouldn't be noticed. So RAID users beware for now.

roman:/local # lsblk 
NAME        MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda           8:0    0   7.3T  0 disk  
└─sda1        8:1    0   7.3T  0 part  
  └─md127     9:127  0   7.3T  0 raid1 /local
sdb           8:16   0   7.3T  0 disk  
└─sdb1        8:17   0   7.3T  0 part  
  └─md127     9:127  0   7.3T  0 raid1 /local
sdk           8:160  1 119.1G  0 disk  
├─sdk1        8:161  1   256M  0 part  
├─sdk2        8:162  1   3.7G  0 part  
└─sdk3        8:163  1     1G  0 part  
sr0          11:0    1 387.6M  0 rom   
sr1          11:1    1  1024M  0 rom   
nvme0n1     259:0    0 953.9G  0 disk  
├─nvme0n1p1 259:1    0   500M  0 part  /boot/efi
├─nvme0n1p2 259:2    0   128G  0 part  [SWAP]
└─nvme0n1p3 259:3    0 825.4G  0 part  /