[will be fixed in 11.4.0-rc3] Failure in qa/specs/features/browser_ui/1_manage/login/register_spec.rb

The registration test fails on staging because registration is disabled.

1) manage standard behaves like registration and login user registers and logs in
     Failure/Error: Factory::Resource::User.fabricate!
     
     Capybara::ElementNotFound:
       Unable to find visible css ".qa-register-tab"
     Shared Example Group: "registration and login" called from ./qa/specs/features/browser_ui/1_manage/login/register_spec.rb:21

TODO:

• Add env var to allow tests to be skipped when signup is disabled: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22205
• Make sure gitlab-qa obeys the flag: gitlab-org/gitlab-qa!183 (merged)
• Add the flag to staging's .gitlab-ci.yml: !4 (merged)