Make cg-common-resource usable in multiple regions

[mogul]

In order to reuse our existing deployment pipeline in other regions. As an operations engineer, I want cg-common-resource to accept a parameter for region.

Acceptance Criteria

• [ ] cg-common-resource takes a parameter for the region to operate in
• [ ] The parameter must be a string containing a valid region code

  Implementation Sketch

Fix this: https://github.com/18F/cg-common-resource/blob/master/command.go#L68

[cnelson]

This is ready for acceptance. Here's the working production CI pipeline:

http://ci.cloud.gov/pipelines/update-cg-common-resource-image