The version follows the same rules as versioning for live media etc.
That means it's always going to be set. The precedence goes like this:
* image specific option
* `kiwibuild_version`
* `global_version`
* `release_version` or `<release_version>_<label_milestone>`.
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>
(cherry picked from commit d351773dab7b3aa8e6de82bbe23058b6b3448dd4)