This doesn't exist for 'nova.volume' and no longer exists for
'nova.network'. There's only one image backend we support, so do like
we've done elsewhere and just use 'nova.image.glance'.
Change-Id: I7ca7d8a92dfbc7c8d0ee2f9e660eabaa7e220e2a
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>