There seems to be an issue with capybara or chromedriver which results
in `fill_in` sometimes appending to an input rather than overwriting
[1], causing some tests to fail under certain circumstances.
Clearing fields before filling them in solves the issue.
Note we're now getting warnings on all tests using the rack driver. I
haven't found a way to avoid the `clear: :backspace` option in
non-JavaScript tests, so to avoid the annoying warnings we should reduce
the number of tests using the rack driver even more.
[1] See issue 2419 in https://github.com/teamcapybara/capybara/issues
de9c261c0e