If (s)testr are killed during a test run (possibly due to a timeout)
they will "leak" a tmp file containing the subunit stream to that point.
This file is useful for debugging so collect it. We don't process it
further as the file is a partial stream and humans may need to look at
it to make sense of it.
Change-Id: I6f0e61ec78f4dd9e2c4e52bc968b4f57586cb22e
8a08cb94ac