[autotest] Only assign server job failures to sheriff on bvt failures.

Some suite are profilic at causing server job failures. Most *real*
server jobs failures will bubble up to the bvts.

TEST=Filed bugs, unittests.
BUG=chromium:293382, chromium:294877

Change-Id: Ic16358c5c1a1eaa31f778807448faefbad583325
Reviewed-on: https://chromium-review.googlesource.com/170027
Tested-by: Prashanth B <beeps@chromium.org>
Reviewed-by: Alex Miller <milleral@chromium.org>
Commit-Queue: Prashanth B <beeps@chromium.org>
1 file changed