Registry v2 mirror support.
Registry v2 mirror support.

The v2 registry will act as a pull-through cache, and needs to be
handled differently by the client to the v1 registry mirror.

See docker/distribution#459 for details

Configuration

Only one v2 registry can be configured as a mirror. Acceptable configurations
in this chanage are: 0...n v1 mirrors or 1 v2 mirror. A mixture of v1 and v2
mirrors is considered an error.

Pull

If a v2 mirror is configured, all pulls are redirected to that mirror. The
mirror will serve the content locally or attempt a pull from the upstream mirror,
cache it locally, and then serve to the client.

Push

If an image is tagged to a mirror, it will be pushed to the mirror and be
stored locally there. Otherwise, images are pushed to the hub. This is
unchanged behavior.

Signed-off-by: Richard Scothern <0a635b283566a554fd91555c968d9ef98402b500@gmail.com>

thaJeztah/distribution,thaJeztah/distribution