Explicitly set version hash to use 7 characters

While 7 is the default number of characters used to abbreviate a commit hash,
this is not (by default) constant and different instances of the same repo may
generate different version strings as a result. This commit sets this length
explicitly to 7 in both package.sh and build-image scripts.

package.sh

@@ -21,7 +21,7 @@ elif [ $CI_COMMIT_BRANCH ]; then
   VERSION_NAME="$CI_COMMIT_REF_SLUG-$CI_COMMIT_SHORT_SHA"
 # if not ci, try to use git
 elif command -v git &> /dev/null; then
-  VERSION_NAME=$(git describe --always --tags --dirty)
+  VERSION_NAME=$(git describe --always --tags --abbrev=7 --dirty)
 # fallback
 else
   VERSION_NAME="latest"