Depend on fdisk | util-linux (<< 2.29.2-3~)

As recently announced on debian-devel-announce
(https://lists.debian.org/debian-devel-announce/2017/08/msg00005.html)
packages who need any of sfdisk, cfdisk or fdisk will need to add
a dependency on the new fdisk package.

Closes: #872219
Thanks: Andreas Henriksson <andreas@fatal.se>