Issue Type: Docker Swarm native, swarm worker not able to pull image from private registry
OS Version/Build: Red Hat Enterprise Linux Server release 7.4 (Maipo)/Docker version 1.12.6, build ec8512b/1.12.6
we want to setup private registry to host our own application images, if a repository having public access we could create a services using docker service command but when we change it to private we can not run docker service command eventhough given full access repo wrt user.