Refactor test to ensure repos are only tagged once.

This was never a bug, but now the test will catch it if it becomes so.
Require 'BUILD_NUMBER' sooner for run_publish_ci
Books must now specify their own github_repo in config.yml.

- We use this for tagging repos, and name-spacing S3 builds.
- Bookbinder complains more eloquently when Cloud Foundry credentials are missing.
- A missing $BUILD_NUMBER will raise an error, sooner.
Bump version to 0.0.11