Set up generally useful stuff:
* chai.should()
* logger stubs
* globals in SandboxedModule, including Buffer and process, which are
now required in Node 12
- move setting into clsi.docker namespace
- rename the variable for images to allowedImages / ALLOWED_IMAGES
- add an additional check for the image name into the DockerRunner
Co-Authored-By: Brian Gough <brian.gough@overleaf.com>