Clusters first request in non visible page is not updating the UI

Our clusters.js script is fetching an endpoint but not doing anything with the data, see https://gitlab.com/gitlab-org/gitlab-ce/blob/bba020a56cbedd6403b637ec7f9eaee258eb7c67/app/assets/javascripts/clusters.js#L79

The actual intentions were:

• Only poll when page becomes visible
• Get data once for any scenario

---

From discussion here, https://gitlab.slack.com/archives/C7FGZRDTK/p1509427497000104