Handle a cluster without public IP Address

[armaseg]

As @dkamenov suggested on #7: when you are running in a VPC, "there really isn't any need to assign a public IP". So, you can change in the LauchConfig the parameter "AssociatePublicIpAddress": "false", nevertheless, as you don't have a public IP, the HOSTNAME parameter used to create the docker image will be resolved as "unavailable".