Implement standard container tests

[king-alexander]

💡 Summary

Modify the standard container tests to work in this repository.

Motivation and context

The standard test harness doesn't play nice with the way Admiral is composed. The configuration expects a main container and version container from which to derive tests. But that causes complications.

Admiral's composition does not have a main container. Instead, a template is used to replicate workers. Because there is no main container, it's not possible for the tests to verify an output or clean exit. We need to find a way to test the replica containers instead.

Implementation notes

• 5 should reference which tests need to be implemented.

Acceptance criteria

• [ ] The main container tests inherited from skeleton-docker have been implemented and fully pass.
• [ ] Per cisagov/admiral#45, there exists a test to verify certificate records are saved to a database.

[king-alexander]

Waiting to merge #5 before I begin work on this issue.