Like 8c62b063, d17f1f5f and e8461571 - pristine copy from omnibus-gitlab
8.5.1+ce.0-1-ge732b39 .

Changes are in

    - gitlab.yml.erb, unicorn.rb.erb

      * Something related to relative URL root (we do not use)
      * Something related to SAML (we do not use)
      * Misc

    - nginx-gitlab-http.conf.erb

      * SPDY -> HTTP/2
      * Relative URL root
      * Configurable proxy_set_header passing

The following files stay the same:

    - database.yml.erb
    - gitconfig.erb
    - gitlab-rails-config.ru.erb
    - gitlab-shell-config.yml.erb
    - nginx.conf.erb
    - rack_attack.rb.erb
    - resque.yml.erb
    - smtp_settings.rb.erb