When parsing a container input, add the checksum to the data as well.
Usually with other inputs, the stage only needs to know the filepath
where it can find the source content. In most (all, so far) cases, this
is a checksum appended to the content type.
In this case, the filepath is the location of the storage bind mount and
the checksum is needed to retrieve the container. The name might only
be a destination name (a name to use for storing the container in the
image), so we can't rely on it being valid in the source.
423819a80e