use rack_driver only in one run in clients_test: all_needed_actions_are_available_in_the_index

runtime with chrome_headless driver:

Finished in 35.536690s, 0.0281 runs/s, 0.3940 assertions/s.
1 runs, 14 assertions, 0 failures, 0 errors, 0 skips

runtime with rack_driver:

Finished in 2.574729s, 0.3884 runs/s, 5.4375 assertions/s.
1 runs, 14 assertions, 0 failures, 0 errors, 0 skips