swapoff: swapoff swap files by LABEL and UUID

 # swapon --show=NAME,UUID
 NAME                   UUID
 /dev/sda3              8d52fca3-bf48-41d6-b826-2315e518a305
 /home/fs-images/2g.img 6fa72b96-b802-441f-a31c-091d65c0212c

 # swapoff UUID=6fa72b96-b802-441f-a31c-091d65c0212c
 swapoff: cannot find the device for UUID=6fa72b96-b802-441f-a31c-091d65c0212c

Reported-by: Sami Kerola <kerolasa@iki.fi>
Signed-off-by: Karel Zak <kzak@redhat.com>
tests: update fdisk tests

Signed-off-by: Karel Zak <kzak@redhat.com>