Deployment state bucket will conflict if used elsewhere

[cdriehuys]

The deployment tool has a goal of being portable(-ish) but currently hardcodes the name of the bucket to store deployment state in. It should be configurable during the bootstrapping process.

Caveats

1. If configurable, it becomes much easier to accidentally separate deployment states and end up with deployments from different machines "fighting" each other.
2. We need some way to pass the state bucket to our Terraform configurations. Perhaps omitting the backend configuration from our Terraform files and creating an environment-specific backend.tf file during the deployment process could solve this.