Comment 1 for bug 1569514

This happens due to new version of pbr 1.9.0 (pbr>=1.6 (from oslo.serialization>=1.4.0->-r requirements.txt (line 16)))
Everything is fine with pbr==1.8.1 https://ci.fuel-infra.org/job/verify-fuel-web-docs/13448/consoleFull
I'm going to have a closer look at the issue to identify a root cause.