Automated testing

[lance]

We need better automated testing for our builders. When I am making changes to them, or creating a new one, I always do some manual testing that involves something like this.

• Create a new builder image with my changes
• Rename it to something non-colliding, e.g. docker tag quay.io/boson/faas-nodejs-builder:tip func-builder
• Create a new function project to test the builder. func create test-func
• Run pack build testproj --builder test-func -v --trust-builder --pull-policy never
• Run docker run --rm -it --entrypoint /bin/sh test-func
• Examine /workspace on the image and be sure it's what I expect. Maybe even npm run or something.
• Change the builder field in func.yaml to func-builder (or whatever I named it)
• Run func build and func run to ensure that it works as expected with func

We need to automate a process similar to this and running it in CI.