Fix import job to provide valid disk-formats list to tempest

Recent changes does not allow image conversion to convert an image
having AMI disk format for image. Passing list of disk-formats to
each import job which will now use qcow2 as default disk-format to
create the image.

Change-Id: I712b304ebe168705ec2793626f5d64135ad6d458
(cherry picked from commit 244ccb68dd)

.zuul.yaml

@@ -235,6 +235,7 @@
           "$TEMPEST_CONFIG":
             image:
               image_caching_enabled: True
+              disk_formats: qcow2,ari,aki,vhd,vmdk,raw,ami,vdi,iso,vhdx
 
 - job:
     name: glance-centralized-cache