Like f6f97d72 - pristine copy from omnibus-gitlab 8.8.7+ce.1-0-g5116476

Changes are:

    - gitlab.yml.erb
      Add gitlab_default_projects_features_container_registry variable to be used by docker containers

    - nginx.conf.erb
      Docker related password storage
      https://gitlab.com/gitlab-org/omnibus-gitlab/issues/1218 (commit f74472d4)

    - rack_attack.rb.erb
      Disable Rack Attack throttling if admin disables it in config file

    - smtp_settings.rb.erb
      If authentication is not enabled for smtp, don't place it in the config.

The following files stay the same:

    - database.yml.erb
    - gitconfig.erb
    - gitlab-shell-config.yml.erb
    - nginx-gitlab-http.conf.erb
    - resque.yml.erb
    - unicorn.rb.erb