Switch from tox to nox

Recent tox releases have put us on a config treadmill. Avoid these
issues entirely by using nox. Nox is a tox alternative that uses
standard tools like pip and should be simpler to use for us.

Change-Id: Ifce288808f535b5ee071dddc597ef54a6d3d03bb
Depends-On: https://review.opendev.org/883664
diff --git a/setup.cfg b/setup.cfg
index 73ab438..e14db8b 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -32,3 +32,10 @@
     update-blueprint = jeepyb.cmd.update_blueprint:main
     update-bug = jeepyb.cmd.update_bug:main
     welcome-message = jeepyb.cmd.welcome_message:main
+
+[flake8]
+# E125 and H are intentionally ignored
+# W503 is a mistake in flake8
+ignore = E125,H,W503,W504
+show-source = True
+exclude = .venv,.tox,.nox,dist,doc,build,*.egg