1129817 - prepend process id and thread id if line is split

By including a unique identifier, it is possible to separate logs that are generated at the same time.

 [Bugzilla-1129817](https://bugzilla.redhat.com/show_bug.cgi?id=1129817)
At this part of the code, the remaining message is still longer than max_length, so the relative_ending_index should only rely on the max length and message id. This isn't clear though, I will add some better comments.