Note that this does not allow uploading under new tags; Docker Registry
requires the tag to be present within the manifest, i.e. we might need
to modify the (possibly signed) manifest.
For now, uploading manifests only identified by a digest is sufficient
for the Atomic Registry; tagging happens in OpenShift imagestreams.
The dockerClient encapsulates makeRequest and authentication setup, and
will be shared between the pull and push code.
This is only a restructuring, does not change behavior.
The dockerImage->dockerImageSource->dockerClient inclusion chain is
somewhat ugly, hopefully eventually we will move the remaining
dockerImage functionality either to dockerutils or to the top level, and
then eliminate it.
Call dockerImageSource.ping() in .makeRequest() if needed, instead of
expecting a caller to do it (which only happened in GetManifest).
This required splitting the URLs into the baseURL (dependent on .ping()
result) and the suffix (independent of it), which was a simplification
anyway.
Also rename WWWAuthenticate to wwwAuthenticate, it is a private cache
field.
This will hopefully allow better reuse of the "copy images" code from
docker.go in the future.
No behavior change, the dirImageDestination code was based on the code
this commit is replacing.
The ImageSource type does not provide all of the functionality of
docker.go, but we will be able to reuse the ImageSource parts in an
OpenShift client.
This is only a restructuring, does not change behavior.
