Switch from docker to container namespace
    
    Fedora Atomic WG has decided to move from the "docker" namespace to
    the "container" namespace for the sake of making it more generic in
    order to target all OCI Compliant container runtimes instead of
    a specific implementation. This update changes what is necessary for
    to the base image metadata as well as add a transitional second call
    to handle both the docker and container namespace for block_retired.
    
    Signed-off-by: Adam Miller <maxamillion@fedoraproject.org>