Concourse deployment of the S3 broker

[mogul]

• [x] Create reusable broker pipeline in Concourse - https://github.com/18F/cg-s3-service-broker/pull/1
• [x] Deploy to production after acceptance tests pass on staging - https://github.com/18F/cg-s3-service-broker/pull/1
• [ ] Deploy to govcloud cf

[mogul]

Please retroactively go through the skipped Grooming steps so we have an idea how we'll know when this is done and how we'll plan to demo it.

[afeld]

Moving remaining work to https://github.com/18F/cg-atlas/issues/25#issuecomment-224368518.