Test fixtures should be built locally with the git-asdf1234 tags

[carmstrong]

Currently, test-postgresql and test-etcd are built as an automated build on Docker Hub. mock-store is built and pushed manually.

In #1351, we added an optimization to only pull these images if they don't already exist. For changes to test-postgresql or test-etcd, this means that we'll continue to use the old images until someone manually nukes the images on the test boxes.

All three of these test fixtures should be refactored to:

• Not push to Docker Hub (disable automated builds)
• Build locally with the same git-asdf1234 hash as the rest of the components
• Use the git-asdf1234 image name in test runs, ensuring we always use the latest version