Failure to make published images public may result in duplicate private images/snapshots
If for some reason we are unable to set a published image to "public" status, it (and its snapshot) remains as a private image. The next attempted publish of the same image will copy a new snapshot/image alongside the previous one.
Setting "public" will fail if the number of public images in the region is already at quota.
The publish code should detect this failure and remove the not-fully-published image/snapshot.