Support pulling Docker images with V2 Schema 2 image manifest

MESOS-3505 added support for pulling Docker images by their digest to the Mesos Containerizer provisioner. However currently it only works with images that were pushed with Docker 1.9 and older or with Registry 2.2.1 and older. Newer versions use Schema 2 manifests by default. Because of CAS constraints the registry does not convert those manifests on-the-fly to Schema 1 when they are being pulled by digest.

Compatibility details are documented here: https://docs.docker.com/registry/compatibility/
Image Manifest V2, Schema 2 is documented here: https://docs.docker.com/registry/spec/manifest-v2-2/