Fix disk_formats in ceph job tempest config

Tempest currently defaults to disk_formats[0] for images it creates,
which is 'ami'. However, it's actually using a qcow2 disk image by
default, which means we're lying to glance when we create those.

Change-Id: I737e9aa51c268a387f1eed24cf717618d057d747
(cherry picked from commit c0ff238)
(cherry picked from commit 62b3192)
(cherry picked from commit 625a10f)

Author: kk7ds

.zuul.yaml

@@ -624,6 +624,8 @@
               manage_locations: true
             volume:
               volume_size: 1
+            image:
+              disk_formats: qcow2,ari,aki,vhd,vmdk,raw,ami,vdi,iso,vhdx
         post-config:
           $NOVA_CONF:
             libvirt: