Add Registrator and Consul Agent to ECS hosts

[bryantrobbins]

This setup will allow Docker containers to register with Consul as they come up:
https://aws.amazon.com/blogs/compute/service-discovery-via-consul-with-amazon-ecs/

[bryantrobbins]

These are added as cloud-init steps to the ECS Cluster Launch Configuration. Tested end-to-end.

May want to look at moving this into Puppet configuration down the road, as this would be at least a bit more cloud-agnostic (even though we are very tied to ECS at the moment).