Install envconsul
Read/write prefixed consul keys for Riak CS
Use envconsul to write docker-reg.env
Configure Docker Reg container run entirely within systemd unit file

systemd will also trigger envconsul to build the env-file for the reg.
Vendor in docker_pull module from modcloth-labs/ansible-docker-pull
Ignore images.json
Add docker pull steps for all images
Move all container config into systemd unit files