Preparing docker images for integration tests

Our test suite relies heavily on custom docker images for testing. The main reason that we use custom images is test speed: having prepared docker images vs. building them on each test execution saves a ton of time.

Adding a new image is relatively straightforward process. We can just copy one of the preexisting definitions from the docker directory and update it. All docker files should have a name in the format of <name>-<tag>.docker.

To build and publish our image, we can run the docker/ script:

$ cd docker
$ ./ sensu-5.21.0.docker

Note that the command will add a sensu-go-tests- prefix to all images. In the previous example, the build script will build the image.