mockchain fails on Fedora 30 since createrepo prints to stderr by default

[cheese]

Short description of the problem

On Fedora 30 with createrepo_c-0.12.2-1.fc30.x86_64, createrepo prints to stderr by default. And mockchain determines createrepo failure by its stderr output. So mockchain always fails.
It seems better to test createrepo exit code instead.

Output of rpm -q mock

mock-1.4.14-1.fc30.noarch

Steps to reproduce issue

1. Run mockchain with -l option

[xsuchy]

Indeed, nice catch.

[xsuchy]

I temporary remove the sys.exit() when we createrepo_c prints something to STDERR.
Mockchain will still print the error (which may confuse user), but it will proceed further. I will talk to createrepo_c about this. I will leave this open until the final solution, but this error is no more fatal.

[praiskup]

Almost year from last update. I'd propose to close this. The mockchain.py code
disappeared, and now we only react on exit status. Which is exactly what this
issue was about.... there's --error-exit-val createrepo_c option. But using that
would be different topic. Feel free to reopen and provide more data what should
happen here.