task hang during create_volume_from_snapshot

[John Haan]

If we progress CinderVolumes.create_volume_from_snapshot with do_delete arguments, the task will hang forever.

The reason is that the source code tries to delete snapshot first before cloned volume from snapshot.

However the snapshot cannot deleted because of cloned volume.

We need to change the step of deleting snapshots and volumes.

from
    self._delete_snapshot(snapshot)
    self._delete_volume(volume)

to
    self._delete_volume(volume)
    self._delete_snapshot(snapshot)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/417334