Enable the overlay fs for Docker on Ubuntu 15.04

Enable overlay fs in docker on Ubuntu 15.04

systemctl stop docker

# kill all old images etc
rm -rf /var/lib/docker

# change the startup options for docker service
mkdir /etc/systemd/system/docker.service.d
cd /etc/systemd/system/docker.service.d
vi storage.conf  

# add the startup option to storage.conf which rewrites the ExecStart with options 
#  NOTE: should be same as /lib/systemd/system/docker.service without aside from the storage option
[Service]
ExecStart=
ExecStart=/usr/bin/docker daemon -H fd:// --storage-driver=overlay

# reload config changes
systemctl daemon-reload

systemctl stop docker

# verify new storage driver
docker info