New API to restore image

At the moment, glance supports the delaying of image data from the store (backend) by setting the ``delayed_delete`` option to `True` in glance-api.conf and when image gets deleted, it actually keeps image data in the backend, and then Scrubber daemon deletes it permanently later. To restore the image, the deployer needs to pass the UUID of that image as 'restore' command line input argument to the glance-scrubber utility and needs to make sure glance-scrubber daemon is stopped before restoring the
image to avoid image data inconsistencies. In short, deployer/administrator/operator needs to interrupt the scrubber daemon to restore the image and trigger it again once the restore operation is complete.