Builders with different Mock version and different results

[Vít Ondruch]

I wonder why different builders has different version of mock and why
the build result differs?

The scratch build passes:

https://koji.fedoraproject.org/koji/taskinfo?taskID=33303459

While the official fails:

https://koji.fedoraproject.org/koji/taskinfo?taskID=33303270


Also, I wonder what is this "BUILDSTDERR:" I don't think the output goes
to stderr nor it makes the output more readable :/


Vít