gitlab:check to be done after nginx

Once you do the more thorough check
`sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production`

you get the following errors since nginx is not yet installed/running:
```
Running /home/git/gitlab-shell/bin/check
Check GitLab API access: /usr/local/lib/ruby/2.0.0/net/http.rb:878:in `initialize': Connection refused - connect(2) (Errno::ECONNREFUSED)
	from /usr/local/lib/ruby/2.0.0/net/http.rb:878:in `open'
	from /usr/local/lib/ruby/2.0.0/net/http.rb:878:in `block in connect'
	from /usr/local/lib/ruby/2.0.0/timeout.rb:52:in `timeout'
	from /usr/local/lib/ruby/2.0.0/net/http.rb:877:in `connect'
	from /usr/local/lib/ruby/2.0.0/net/http.rb:862:in `do_start'
	from /usr/local/lib/ruby/2.0.0/net/http.rb:851:in `start'
	from /home/git/gitlab-shell/lib/gitlab_net.rb:62:in `get'
	from /home/git/gitlab-shell/lib/gitlab_net.rb:29:in `check'
	from /home/git/gitlab-shell/bin/check:11:in `<main>'
gitlab-shell self-check failed
  Try fixing it:
  Make sure GitLab is running;
  Check the gitlab-shell configuration file:
  sudo -u git -H editor /home/git/gitlab-shell/config.yml
  Please fix the error above and rerun the checks.
```

Should we do the more thorough gitlab:check after nginx is installed?  Once I had nginx up and running, I no longer received the errors.