Base url generation doesn't take into account HTTP/HTTPs access

Summary

Base url generation doesn't take into account HTTP/HTTPs access

Steps to reproduce

Setup gitlab-ce as: network: Internet -https-> proxy -http-> docker instance No external_url defined

Expected behavior

Go to a build page: https://FQDN/user/project/builds/36 Console shows build output

Actual behavior

Console keeps on turning (no output). Why ? The browser tries to fetch http://FQDN/user/project/builds/36.json instead of https://FQDN/user/project/builds/36.json (HTTP vs HTTPs) and it doesn't work because of security concerns.

When accessing the url manually it works. So it's purely a problem of detecting if the url is HTTP or HTTPs

Results of GitLab environment info

GitLab 8.13.3

GitLab Shell 3.6.6

GitLab Workhorse 0.8.5

GitLab API v3

Git 2.7.4

Ruby 2.3.1p112

Rails 4.2.7.1

PostgreSQL 9.2.18