[autotest] Make gs_offloader exit on ctrl-c.

Python creates all threads by default in such a way that they will keep
the program running until they end. By setting the |daemon| flag on a
thread before starting it, Python will now kill the program when no
non-daemon threads are running (which happens if/when the main thread
exits).

BUG=None
TEST=ctrl-c'ing gs_offloader makes it exit

Change-Id: I6a55c008fef0561f8b5ee10ba4300c2d8559615a
Reviewed-on: https://gerrit.chromium.org/gerrit/40505
Tested-by: Alex Miller <milleral@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Alex Miller <milleral@chromium.org>
1 file changed