support multiple image backends for libvirt driver
Registered by
Zhou Yu
Currently, the cloud administrator can not choose ephemeral storage backend
device (e.g. SSD or non-SSD) and driver (e.g. qcow2 or ceph) for per flavor.
The lack of these features restrict the price strategy for different
performance and functional requirements. So we should add support to
configure multiple libvirt image backends, and then in the flavor
indicate which backend should be used for per instance.
Whiteboard
(?)
