Adding Cinder backend storage driver to Glance

This change allows Glance drive Cinder as a block storage backend to
store image data.
Before this we already use swift as an object storage backend to save
image.

Currently the patch is a partial implementation, after Cinder expose
'brick' library, 'host-volume-attaching' and 'multiple-attaching'
enhancement ready, the store will support ADD/GET/DELETE interface
finally.

blueprint: glance-cinder-driver

Change-Id: I4cdeccdb518972c0280e59c984ed6b001dafe243
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>