lsblk: add --dedup <column>

lsblk: add --dedup <column>

The target use-case are systems with large number of multi-path
devices or systems with duplicate (copied) filesystems.

The feature is flexible enough to use arbitrary column (for example
WWM or UUID, ...) as de-duplication key.

For example tree with multi-path devices sd{c,d,e,f}

./lsblk
NAME        MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda           8:0    0 223.6G  0 disk
├─sda1        8:1    0   200M  0 part  /boot/efi
├─sda2        8:2    0   200M  0 part  /boot
├─sda3        8:3    0 130.3G  0 part
├─sda4        8:4    0    50G  0 part  /
└─sda5        8:5    0  42.9G  0 part
sdb           8:16   0  74.5G  0 disk
└─sdb1        8:17   0  74.5G  0 part  /home/archive
sdc           8:32   0   100M  0 disk
└─mpatha    253:0    0   100M  0 mpath
  ├─mpatha1 253:1    0    50M  0 part
  └─mpatha2 253:2    0    49M  0 part
sdd           8:48   0   100M  0 disk
└─mpatha    253:0    0   100M  0 mpath
  ├─mpatha1 253:1    0    50M  0 part
  └─mpatha2 253:2    0    49M  0 part
sde           8:64   0   100M  0 disk
└─mpatha    253:0    0   100M  0 mpath
  ├─mpatha1 253:1    0    50M  0 part
  └─mpatha2 253:2    0    49M  0 part
sdf           8:80   0   100M  0 disk
└─mpatha    253:0    0   100M  0 mpath
  ├─mpatha1 253:1    0    50M  0 part
  └─mpatha2 253:2    0    49M  0 part

De-duplicate by WWN:

./lsblk -M WWN
NAME        MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda           8:0    0 223.6G  0 disk
├─sda1        8:1    0   200M  0 part  /boot/efi
├─sda2        8:2    0   200M  0 part  /boot
├─sda3        8:3    0 130.3G  0 part
├─sda4        8:4    0    50G  0 part  /
└─sda5        8:5    0  42.9G  0 part
sdb           8:16   0  74.5G  0 disk
└─sdb1        8:17   0  74.5G  0 part  /home/archive
sdc           8:32   0   100M  0 disk
└─mpatha    253:0    0   100M  0 mpath
  ├─mpatha1 253:1    0    50M  0 part
  └─mpatha2 253:2    0    49M  0 part

Addresses: https://github.com/karelzak/util-linux/issues/616
Signed-off-by: Karel Zak <kzak@redhat.com>