Provision a bucket for RDS logs

[spgreenberg]

In order to ship RDS logs to a customer via S3, the broker should be able to provision a bucket if necessary.

Acceptance Criteria

• GIVEN a customer opting in to RDS log shipping to S3
  AND without an existing bucket for RDS logs in the space
  WHEN the customer opts in to ship RDS logs
  THEN the broker provisions an S3 bucket (service instance) in the customer space

• GIVEN a customer opting in to RDS log shipping to S3
  AND with an existing bucket for RDS logs in the space
  WHEN the customer opts in to ship RDS logs
  THEN the broker uses the existing S3 bucket (service instance) in the customer space

---

Security considerations

By leveraging the broker, we minimize any security risks (they are the same with any other S3 bucket). Because the service instance is in the customer space, the customer can generate bindings and service keys as needed.

[markdboyd]

Superseded by

#372
https://github.com/cloud-gov/private/issues/957