Docker image for CI builds

Until now, the CI build used a custom Docker image I made a few years ago, docker-rare. This image has been maintained by @raphael.flores since then.

We now added a few end-to-end tests to the application, using Cypress. To run these tests, we need xvfb on the docker image. As a shortcut, I replaced the base image with an image provided by circleci, that offers a jdk 8, browsers, and vxfb. The image is also maintained up-to-date, and lighter than the one we have.

@raphael.flores mentioned that this probably breaks other jobs like the indexing one.

The long term plan could be:

• to keep the circleci image for test jobs
• to remove docker-rare
• to create a dedicated image (if needed) for the broken jobs. Maybe another image provided by circleci could do the job as well.

An alternative would be to update docker-rare to include xvfb, and keep using it.

Original discussion: 67cfa26e (comment 57210)