Idea: Target Type

[dudleycodes]

Right now, our use case is only for testing Docker images. But in the future we might want to open it up to other types of tests (local CLI utilities, remote CLI over SSH, etc). So, what if expanded the yaml template for target to require a type attribute?

target:
    type: docker-image
    ....

This way, if/when we add new targets, ShellAndTest could be cleanly expanded in that direction?

For now, we could just require target: type: docker-image to be provided. If it's missing, throw an error that target type must be specified, and if it is anything else other than docker-image it throws an error target type x not supported.