this makes it easier to see which chunks are corrupt
(and enables us in the future to build a 'complete' list of
corrupt chunks)
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
And make verify_crc private for now. We always call load_from_reader() to
verify the CRC.
Also add load_chunk() to datastore.rs (from chunk_store::read_chunk())