In order to enforce strict handling of snapshotter values on the
container object, the defaults have been moved to the client side. This
ensures that we correctly qualify the snapshotter under use when from
the container at the time it was created, rather than possibly losing
the metadata on a change of default.
Signed-off-by: Stephen J Day <stephen.day@docker.com>
After some analysis, it was found that Content.Reader was generally
redudant to an io.ReaderAt. This change removes `Content.Reader` in
favor of a `Content.ReaderAt`. In general, `ReaderAt` can perform better
over interfaces with indeterminant latency because it avoids remote
state for reads. Where a reader is required, a helper is provided to
convert it into an `io.SectionReader`.
Signed-off-by: Stephen J Day <stephen.day@docker.com>
