Ci

Initial functionnal

* Tests are located in sharelatex.tests.functionnal

* For now some minimal example of command line calls.
  We only check the return status code

Keyring testing integration

* Use CI_BASE_URL, CI_USERNAME, CI_PASSWORD env var to detect if the
commands are running in the CI context. This allows to create a special
keyring that output CI_PASSWORD as password fot the user.

In a next step we'll want to use a testing framework for that purpose.