import_export: project description lost when importing Gitlab export

Summary

When trying to import projects exported from GitLab 8.15.2 (I tried importing to 8.15.2 and 8.13.8), project description is lost.

Steps to reproduce

1. Go to settings of project in GitLab instance A
2. Click on export, download export tarball when notified
3. Go to GitLab instance B, click on "New project", choose "Gitlab export"
4. Upload tarball.

I verified that description is in project.json in the project tarball, so it's likely a bug in the importer.

I could reproduce the behaviour when trying to import several exports from 8.15.2 on private instances of 8.15.2 and 8.13.8.

Expected behavior

Project shall have original description after import.

Actual behavior

Project description empty after import.