Automate CI docker image builds

[TristanDebrunner]

Right now the builds of new docker images for testing the rust code are being built manually. This is causing errors when the build machine is ARM based, and is generally a large enough effort that the rust version in CI is not always up to date.

The builds should be automated in CircleCI, thereby reducing the effort to build a new version. It also eliminates the architecture based errors, as the same hardware will build the images and run the images for CI testing.

[TristanDebrunner]

Resources:

1. CircelCI guide to building images
2. Guide to logging in to docker CLI in CI
3. Automating when the image is built by CI
4. Another (simpler?) alternative to 3.

[TristanDebrunner]

No longer needed thanks to #195