Update push and pull to registry 2.1 specification

Signed-off-by: Derek McGowan <derek@mcgstyle.net>
Allow private V2 registry endpoints

Signed-off-by: Derek McGowan <derek@mcgstyle.net>
Get token on each request

Signed-off-by: Derek McGowan <derek@mcgstyle.net>
Merge pull request #6 from dmcgowan/v2-registry-pushpull

Update push and pull to registry 2.1 specification