Return the latest finished or running build's info in build_log_json

[lainets]

Currently, the build_log_json return the info for the latest finished update but it would make sense to instead give the info of any running build instead if one exists. The reason why this happens is that the logic selects the update by updated_time but that is only set for finished updates.

I'd say that it would also be better to return a pending build if one exists and no build is running. This should be a very rare occurrence but it would make it clear to the user that a update was received but is just hasn't been started for some reason.