Enable glance-api show_image_direct_url for COW

Enable glance-api show_image_direct_url for COW

Setting `show_image_direct_url` to true allows to enable Copy-On-Write
features when using some storage backends across Nova, Cinder & Glance.
It allows for example nearly instantaneous creation of instances root
disk and volumes when using RBD as a storage backend for all projects by
using Ceph features instead of downloading from Ceph via Glance, then
convert the image, then upload to Ceph via Nova or Cinder.

Change-Id: I1f56273c6b7c8d3922799cae07a66eebc0884205