Improve access check on images
Improve access check on images

Makes sure that users can delete only their own images, snapshots.
Enable listing of all images, both private which are owned and the public
ones. Only list the private images/snapshots for the owner and admin users.
Fixes bug 863305

Change-Id: I7326ec4a99158c8db5319f2397c99c5a89be2cb5

n0ano/ganttclient