Export pull as a public function
Export pull as a public function

It will be helpful to expose the pull implementation which supports
pulling private images for other CLI commands that rely on helper images.

Signed-off-by: Daniel Hiltgen <450e8eee12e8d348f09427c205cd53e1e4ff975a@docker.com>

thaJeztah/cli,docker/cli,cpuguy83/cli,docker/cli,cpuguy83/cli,thaJeztah/cli