如何使用cloud-init安装docker？

I want to create instances in Openstack that will have Docker in them already installed prior to ssh to them. So naturally I got interested in Cloud-init technology because it allows us to install packages on virtual machines during first boot time. So now I'm trying to install Docker on my instances during boot time, here is my code that I'm passing to the user data;I want to create instances in Openstack that wi