The files created in runroot task are owned by root by default (because
that's who is running the processes to create them). Making the results
world readable allows the compose to work, but it still can be difficult
to clean up old composes if they contain random files owned by root.
Fixes: https://pagure.io/pungi/issue/1039
JIRA: COMPOSE-2906
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>