Imports of package transfer

PathSynopsis
contextPackage context defines the Context type, which carries deadlines, cancellation signals, and other request-scoped values across API boundaries and between processes.
github.com/containerd/containerd/content
github.com/containerd/containerd/images
github.com/opencontainers/image-spec/specs-go/v1
ioPackage io provides basic interfaces to I/O primitives.