Add code coverage to the tests

[sylvinus]

Must merge the coverage files of all the worker processes that ran.

[sylvinus]

@antoine-collet can we copy what we do for PA?

[sylvinus]

Added in CircleCI. Still need to merge coverage from worker instances
https://circle-artifacts.com/gh/pricingassistant/mrq/12/artifacts/0/home/ubuntu/mrq/htmlcov/index.html