Schema1 manifests did not set a size in the digest for the blobs,
breaking the expectations of the update http seeking reader. Now
the http seeker has been updated to support unknown size as a
value of negative 1 and the schema1 puller sets the unknown size
accordingly.
Signed-off-by: Derek McGowan <derek@mcgstyle.net>
To support resumable download, the fetcher for a remote must implement
`io.Seeker`. If implemented the `content.Copy` function will detect the
seeker and begin from where the download was terminated by a previous
attempt.
Signed-off-by: Stephen J Day <stephen.day@docker.com>
