Construct 3 docker images: 1 which will be used for tests, 2 which will be used by installation script

- the test image contains all dependencies needed to run the pipeline (except the pipeline itself)
- the install-ubuntu-base image contains only ubuntu, with python3 and pip3 installed. This will be used to check that, in that case, the installation script installs everything
- the install-ubuntu-barrnapOnly contains ubuntu with Python3 and pip3 installed, and barrnap installed, but not prokka. The installation script should install prokka