docker/test: add a pytest based test for the git loading stack
For this, we extract the docker-compose setup in a dedicated fixture. This is needed otherwise one cannot run all tests at once (both scheduler_host and deposit_host conflict on the docker-compose part).
Also no need for most of the fixtures to be session scoped.
In docker/scheduler/entrypoint.sh, run setup_pgsql before setup_pip; this hack is needed to prevent some race conditions in tests where it sometimes happens that the ~/.pg_service file generated by the setup_pgsql bash function is not visible in first calls to scheduler_host.check_output() testinfra helper function.
Running setup_pip after setup_pgsql ensures(?) this does not happen.
Migrated from D2552 (view on Phabricator)