Jeversmann/kochiku yml updates

Changes build enqueueing logic so that test command, on success script, and log file targets from kochiku.yml. I also moved the logic for interacting with the GitRepos around to eliminate cases where methods were making assumptions about how they were being called.
this if condition should be reversed to check build.on_success_script first because that is the cheaper of the two operations.

Also is should be `build.on_success_script.present?` to protect against empty strings.