[tox] Use py.test to run tests In unittest_rqlrewrite.py and repotest.py, rename utility functions so that they are not considered as "test functions" by py.test.

[test] Fix devtools unittest_i18n when ran without pytest There is currently some weird error, requiring both to hack cubicweb.__path__ and to stop using load_module_from_name to load the registry. Introduce a dependency on to-be-released version of logilab common integrating fix for https://www.logilab.org/ticket/6085650 Do some extra import cleanups along the way.

[server] explicitly set postgres LC_MESSAGES variable to C on connection We parse some error messages so we need them to be in English. It's not clear to me exactly when that's not the case, but this fixes running unittest_postgres' "test_constraint_validationerror" with py.test for Sylvain.