[High5][OOBE] FingerprintSetupScreen test changes

Leverage skip_post_login_screens_for_tests in FingerprintSetupScreenTest
so that all screens are skipped after login until the fingerprint setup
happens. Previously, the test was using signin_screen_exit_waiter to
wait until the UserCreation screen. But this waiting was being done
after login had already happened, which is after the UserCreation
screen. Also replace the existing logic for waiting and capturing the
exit result with a base::test::TestFuture.

Bug: b/348326316, b/365059362
Change-Id: I6b2d1c0c1419e51d9e00332c63844392d6d939b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5940566
Commit-Queue: Renato Silva <rrsilva@google.com>
Reviewed-by: Hardik Goyal <hardikgoyal@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1370621}