Fix image killed after deletion

If an image upload fails after the image was deleted during
the upload, the image status currently gets set to 'deleted'
then 'killed' once the upload fails. This patch fixes this so
that if the image was deleted it stays in 'deleted' state.

Permitted from_states for transitioning to 'killed' are
'queued' and 'saving'. We now enforce this transition and
raise an exception if it is violated.

Closes-Bug: 1236868
Co-authored-by: Hirofumi Ichihara <ichihara.hirofumi@lab.ntt.co.jp>
Co-authored-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Change-Id: I5552220ce264c0d09780bbd0eb7610e7cff0b820
Merge "Fix image killed after deletion"