Step: resize-rootfs
-----------------------------------------------------------------------------

Configure the system on the image so that it automatically resizes
itself to fill the actual disk, upon first boot. For this to work, the
root file system MUST be the last partition on the image.

Also, the image MUST have the `parted` package installed for the
`partprobe` command.

Step keys:

* `resize-rootfs` &mdash; REQUIRED; value MUST be the tag for the root
  filesystem.

This is based on reading the changes by Peter Lawler to the
[image-specs](https://salsa.debian.org/raspi-team/image-specs.git)
repository to do the same thing.

Example:

~~~yaml
- resize-rootfs: root
~~~
