When builder plugin loading fails with traceback, there is no info in kojid.log. Last line is simply:
2017-05-23 09:11:39,932 [INFO] koji.build: Loading plugin: runroot
There should be traceback from plugin recorded, or at least note, that loading failed, so server is stopping.
PR #445
Commit 6165d5dd fixes this issue
Commit b5c57561 relates to this ticket
Metadata Update from @tkopecek: - Issue set to the milestone: 1.13
This issue has been migrated to Fedora Forge: https://forge.fedoraproject.org/koji/koji/issues/433
Please continue any further discussion there.