Preserve testr temp files

If testr is killed before it finishes running, it saves its output in a
temp file.  If something times out this file may provide insight into
what was making it slow, so preserve the temp file.

Related-Bug: #1258682

Change-Id: I5cd1bc2326998bf3a1c29cd3773bf583f04ef3d5
Merge "Preserve testr temp files"