This patch makes the tests (including the test driver) run entirely
inside Vagrant, which avoids calling the very slow `vagrant` driver many
times for running the tests. On my machine, `./test` runs in 22 seconds,
down from hundreds of seconds prior to this patch.
This also has the nice side effect of matching how the Travis CI tests
were run, so there's no need for a separate `test_travis` anymore.
Anish Athalye
Benjamin Chrétien