[ci] Increase capybara timeout value to 6

Commit 82380ae decreased the capybara timeout to allow
faster development - test cycles. Since recently we got a couple of test
failures, which might have been caused by this change. And the fact that travis got under higher load. So we have to tweak the value a bit.

Let's see if a timeout of 6 works better for OBS.

src/api/test/test_helper.rb

@@ -40,7 +40,7 @@
 require 'capybara/poltergeist'
 
 require 'capybara/rails'
-Capybara.default_wait_time = 2
+Capybara.default_wait_time = 6
 
 Capybara.register_driver :poltergeist do |app|
   Capybara::Poltergeist::Driver.new(app, debug: false, timeout: 30)