[Files app] UI test refactor the file list refresh logic

Change the UI tests to use keyboard shortcut instead of refresh button
to refresh the file list, because the button can be disabled since
CL:1608962.

Remove some debugging logs that aren't needed anymore.

Format some lines in test_util.js.

Bug: 961244
Change-Id: I92d6feef37278ea16dd0396c3e08550a57491c52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1610662
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Auto-Submit: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659379}
5 files changed