Earlier this could be achieved using DOCKER_OPTS
in the /etc/default/docker
config file which worked on Ubuntu 14:04 and had some issues on Ubuntu 15:04. Not sure if this has been fixed.
The below line needs to go into the file /etc/default/docker
on the host which runs the docker daemon. The change points to the private registry is installed in your local network. Note: you would require to restart the docker service followed with this change.
DOCKER_OPTS="--insecure-registry <priv registry hostname/ip>:<port>"