http+unix client does not set Host header
This seems to be incorrect behavior that was being tolerated by some servers. However, the 8.15 omnibus-gitlab packages use Go 1.7, and it seems like Go 1.7 rejects requests lacking a Host: header.
So the broken HTTP client used for unix sockets in gitlab-shell breaks when used with GitLab 8.15 and gitlab-workhorse.
Hard to tell what the impact is because this is a non-standard configuration. And some people who use the unix socket option use it to connect to Unicorn, not gitlab-workhorse, and Unicorn may not mind the missing Host header.