Implement integration tests

Let's figure out a way to implement integration tests for rdsys. Here's a simple suggestion for a simple shell script:

1. Write a simple cached-extrainfo file to disk.
2. Start the backend.
3. Start the HTTPS distributor.
4. Use curl to fetch bridges from the HTTPS distributor.
5. Make sure that the bridges are the same as those in the cached-extrainfo file.

There are probably smarter ways to accomplish this. Let's make sure that our integration tests are lightweight and can be run as part of a continuous integration test infrastructure.