Better unit test coverage

[Mierdin]

• Automated coverage testing
• at least 80% unit test coverage (do api/server and etcddb first)
• automated integration testing
• Don't forget testlet projects!

There were two continue statements added in PR #2 and I was wondering if some existing functionality would change with this addition. This is a great indicator that this layer is in need of unit testing!

In PR https://github.com/Mierdin/todd/pull/2 I was worried that a change to api/server/groups.go (specifically Groups () and ListObjects()) would break something I was doing to return an empty slice instead of a nil slice, to keep the API more consistent. This indicates to me that this is a prime target for unit testing.