When pushing a different manifest (different sha256) over an existing
tag and trying to pull from it afterwards the client gets an error:
Unknown manifest in registry.
Even if pushing over an existing tag seems like a bad idea, it is
supported by the official docker registry.
The issue is that leftovers from the previous manifest are still present
in the container format folder which causes dlrepo to return an error
(two files matching container/manifests/*/*/*). This was never expected
When uploading a new manifest, make sure to delete everything related to
it (manifest, layers and config) so that only the new files are present
in the container format.