Explore continuous integration for testing the gblstack using goss

[jrgriffiniii]

Currently we are not testing the actual build of the Rails application - perhaps using CircleCI in order to test the validity of the build could improve the stability of this?

There are serverspec alternatives to testing Dockerfile builds on continous integration, and Goss looks like an option for testing the image in https://github.com/geoblacklight/gblstack/blob/master/dockerfiles/rails/Dockerfile.

https://circleci.com/blog/testing-docker-images-with-circleci-and-goss/ leaves me optimistic about CircleCI.