truncate too long log files somewhere in the middle, not at the end

[paulgevers]

We've had this problem at ci.debian.net too, that sometimes log files are just too big. Truncating the log at the end means that a lot of the interesting data there goes missing. Typically the beginning and the end are the more interesting parts of the log, so I suggest to truncate somewhere in the middle.

[kpcyrd]

This is somewhat annoying to implement since log output is handled directly in memory instead of being written to disk.

If a build produces 100s of megabytes of output (or even >= 1 gigabyte) I'd rather have the build be more considerate, since log storage is a shared resource.