Confusing error message

[srfraser]

https://github.com/mozilla-releng/beetmoverscript/blob/master/beetmoverscript/utils.py#L339 ends up looking like a path with a space in it, we should reformat it and check for other similar error messages

[MihaiTabara]

Thanks for filling this. I hit it too last week but failed to file an issue against it. It was indeed extremely confusing to understand what's going on there.