Add support for aki/ari images (#1356)

diff --git a/roles/glance/vars/main.yml b/roles/glance/vars/main.yml
index 7774bb6..37c8c20 100644
--- a/roles/glance/vars/main.yml
+++ b/roles/glance/vars/main.yml
@@ -47,7 +47,7 @@
         connection_recycle_time: 10
         max_pool_size: 1
       image_format:
-        disk_formats: "qcow2,raw"
+        disk_formats: aki,ari,qcow2,raw
       oslo_messaging_notifications:
         driver: noop
   manifests: