When migrating from Casper to Puppeteer, some tests
were missed for adding log-out calls at the end.
This commit adds log-out calls to those missed tests.
Also, As we are resetting the test database after each
run (from 99f8be6a12) it will better to log out because we are
not resetting Tornado's internal state. It'd help us prevent
any future flakes.
This commit works around an issue with Puppeteer tests on Firefox
where `page.url()` does not show the URL fragment, by adding a
temporary function that solves the issue.
Note that at this point, it's not possible to create moderator users;
this just will make it easier to write tests for logic involving them
as we develop the feature.
