Imports of package cache

PathSynopsis
fmtPackage fmt implements formatted I/O with functions analogous to C's printf and scanf.
github.com/docker/distributionPackage distribution will define the interfaces for the components of docker distribution.
github.com/docker/distribution/contextPackage context provides several utilities for working with Go's context in http requests.
github.com/docker/distribution/digest
testingPackage testing provides support for automated testing of Go packages.