tox.ini: Run tests through pifpaf

We need the postgres dependency to run the tests

tox.ini

@@ -5,8 +5,9 @@ envlist=flake8,py3
 deps =
   .[testing]
   pytest-cov
+  pifpaf
 commands =
-  pytest --cov=swh --cov-branch {posargs}
+  pifpaf run postgresql -- pytest --cov=swh --cov-branch {posargs}
 
 [testenv:flake8]
 skip_install = true