Add ability to deactivate an image

If a questionable image is present in a deployment, admins may
want to prevent use of the image until further investigation.
This patch provides the ability to 'deactivate' an image by
providing two new API calls and a new image status 'deactivated'.
Attempting to download a deactivated image will result in a
403 'Forbidden' return code.

Change-Id: I32b7cc7ce8404457a87c8c05041aa2a30152b930
Implements: bp deactivate-image