* Upgrade tox to a newer version (a least 3.18.0 like nova)
* Stop using run_tests.sh (use prepare_db.sh and stestr directly)
* Add venv and mistral.log in gitignore
Change-Id: I71c206aadc4133932fb591376b020a39a78d837d
Signed-off-by: Arnaud M <arnaud.morin@gmail.com>