Let exception ImportError be raised (run-tests)

See https://discuss.tryton.org/t/should-run-tests-report-something-on-import-error-of-modules/2748

When using run-tests ImportErrors are caught in tryton_test.py modules_suite. These errors are relevant for development and help correct mistakes when writing tests.

It seems that this exception is not raised for historical reasons and we could just let it be raised now.

Added an issue and submitted a patch Issue 9359: Let exception ImportError be raised (run-tests) - Tryton issue tracker

It makes sense for me. It wil be great if you can propose a patch for it.