[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

bin/buildpkg.in

@@ -151,7 +151,7 @@ eval_build_list "${list_dir_pkg}" "${build_list_pkg}"
 
 prepare_dir "${pkg_dir}"
 
-chown ${OWNER}:${OWNER} "${pkg_dir}"
+chown ${OWNER}:$(id --group ${OWNER}) "${pkg_dir}"
 
 init_base_devel
 

lib/util-iso.sh

@@ -597,7 +597,7 @@ compress_images(){
 	local timer=$(get_timer)
 	run_safe "make_iso"
 	make_checksum "${iso_file}"
-	chown -R "${OWNER}:users" "${iso_dir}"
+	chown -R "${OWNER}:$(id --group ${OWNER})" "${iso_dir}"
 	${sign} && sign_iso "${iso_file}"
 	show_elapsed_time "${FUNCNAME}" "${timer}"
 }