Merge: Continuous integration tests for Nitcorn

Test some of the main nitcorn features for regression. This would have caught the last bugs we experienced with nitcorn: #2023, the binary file bug, the file server directory access without the final /, etc. This structure could be used to add more tests in the future, for new or forgotten features and for existing clients like Tnitter and Opportunity.

Pull-Request: #2031
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>