gitignore: Ignore reno artefacts
gitignore: Ignore reno artefacts

Change-Id: I27a3689c2e22452c082764eed8d26cd8f3bbcd13
Signed-off-by: Stephen Finucane <492121341a95b3c3aab646bed44634f739dd019b@redhat.com>

openstack/cliff,openstack/cliff