losetup: add --set-capacity

losetup: add --set-capacity

The LOOP_SET_CAPACITY allows to resize loop device size.

Example:

 # blockdev --getsize64 /dev/loop0
 10485760

 # dd if=/dev/zero of=/home/images/aaa.img count=10 bs=1M oflag=append conv=notrunc

 # blockdev --getsize64 /dev/loop0
 10485760

 # ./losetup --set-capacity /dev/loop0

 # blockdev --getsize64 /dev/loop0
 20971520

CC: J. R. Okajima <hooanon05@yahoo.co.jp>
Signed-off-by: Karel Zak <kzak@redhat.com>