[util-*] use given primary group of user in chown cmd

- don't assume that the primary group of a user is named the same as the user itself
- fixes https://github.com/manjaro/manjaro-tools/issues/248

lib/util-iso.sh

@@ -611,7 +611,7 @@ compress_images(){
 	make_checksum "${iso_file}"
 	${sign} && sign_iso "${iso_file}"
 	${torrent} && make_torrent
-	chown -R "${OWNER}:${OWNER}" "${iso_dir}"
+	chown -R "${OWNER}:$(id --group ${OWNER})" "${iso_dir}"
 	show_elapsed_time "${FUNCNAME}" "${timer}"
 }
 

lib/util-pkg.sh

@@ -250,7 +250,7 @@ move_to_cache(){
 	mv $src ${pkg_dir}/
 	${sign} && sign_pkg "${src##*/}"
 	[[ -n $PKGDEST ]] && rm "$1"
-	chown -R "${OWNER}:${OWNER}" "${pkg_dir}"
+	chown -R "${OWNER}:$(id --group ${OWNER})" "${pkg_dir}"
 }
 
 archive_logs(){