partx: add --sector-size option

partx: add --sector-size option

/dev/sdc is 4K disk:

 # fdisk -l /dev/sdc
 Disk /dev/sdc: 100 MiB, 104857600 bytes, 25600 sectors
 ...
 Device     Boot Start   End Sectors Size Id Type
 /dev/sdc1        1024 25599   24576  96M 83 Linux

let's use it as disk image:

 # dd if=/dev/sdc of=~/sdc.img
 # losetup -f ~/sdc.img

old version:

 # partx --show /dev/loop0
 NR START   END SECTORS SIZE NAME UUID
 1  1024 25599   24576  12M      6a4ba75b-01

new version:

 # partx --show /dev/loop0 --sector-size 4096
 NR START    END SECTORS SIZE NAME UUID
  1  8192 204799  196608  96M      6a4ba75b-01

Addresses: https://github.com/karelzak/util-linux/issues/396
Signed-off-by: Karel Zak <kzak@redhat.com>