Use filter-output for blhc job and return artifacts for piuparts

The output for blhc was reported to exceed the job's log limit for some packages. Using filter-output and providing the logs as artifacts should resolve this issue.

Additionally, the piuparts job already used filter-output but did not output the logs as artifacts. We now provide the logs as artifacts for piuparts as well, since using filter-output assumes the log limit might be exceeded.

In reprotest job, reprotest.log was used as the output file name, so we followed the same convention with blhc and piuparts.

Implements #225 (closed), closes #299 (closed)