Unicorn timeout during import of large Gitlab export

Setup: self-hosted Gitlab 8.11.0 on Debian 8.5, using the Omnibus package

Steps to reproduce:

1. Create and download an export of a big (>1GB) project
2. Enable "Gitlab export" as import source in /admin/application_settings
3. Create a new project, enter a name and choose "Gitlab export" as source
4. Select the downloaded export and submit it
5. After the upload is finished (takes several minutes), the Unicorn worker runs into the default 60s timeout, and I see a 502 error

As a workaround I've added unicorn['worker_timeout'] = 600 to our gitlab.rb which allowed me to successfully complete the process.

I found this old issue which raised a timeout from 4 minutes to 15 minutes, but it looks like that's a different importing process.