Shave spec/features/issues/filtered_search/dropdown_label_spec.rb from 10 minutes to 1.5 minutes

- Don't use `sleep` (most of the time was wasted by that)
- Expect some elements to be visible instead: capybara is smart enough
  to retry a few times if it cannot find an element
- See
  https://github.com/teamcapybara/capybara#asynchronous-javascript-ajax-and-friends
- Don't create unneccessary DB records
- Group some examples together to shave some setup time (where it makes
  sense)
Signed-off-by: Rémy Coutable <remy@rymai.me>

spec/spec_helper.rb

@@ -35,6 +35,7 @@ RSpec.configure do |config|
   config.include Warden::Test::Helpers, type: :request
   config.include LoginHelpers, type: :feature
   config.include SearchHelpers, type: :feature
+  config.include WaitForAjax, type: :feature
   config.include StubConfiguration
   config.include EmailHelpers, type: :mailer
   config.include TestEnv