factory_flow: Use SIGINT to terminate servers.

And if a server does not stop in five seconds, send SIGKILL to
kill it.

BUG=chrome-os-partner:26795
TEST=manually on my host

Change-Id: Ib2b650350b508a7da3d537e940b464f8809dbabe
Reviewed-on: https://chromium-review.googlesource.com/199055
Reviewed-by: Ricky Liang <jcliang@chromium.org>
Commit-Queue: Ricky Liang <jcliang@chromium.org>
Tested-by: Ricky Liang <jcliang@chromium.org>
1 file changed