ENH: aws_docker_cluster module

[mplanchard]

Adds an aws_docker_cluster module, which takes care of managing the following resources:

• aws_cloudformation_template - using the standard Docker template and passing appropriate variables through
• SSH Keypair for connecting to cluster managers (optional, can also use existing keypair)
• VPC peering connection and routes from the docker cluster to another specified cluster (optional)
  • Security group on the peered VPC, if specified, for defining cluster rules
• DNS record pointing to the docker cluster (optional)

[mplanchard]

I'll go ahead and create a v1.0.0a1 tag upon merging