devil: accept `pkill host_forwarder` exiting with a 1.
devil: accept `pkill host_forwarder` exiting with a 1.

Bug: chromium:1038789
Change-Id: Ia4a9706ae0263db7f663bcf79ec5afe5ba2b28ad
Reviewed-on: https://chromium-review.googlesource.com/c/catapult/+/2192510
Reviewed-by: Haiyang Pan <a4f2e84c8a17b76158e6fd7337357be2539c5573@google.com>
Commit-Queue: John Budorick <17d38a2d68c6a07a3ab0ce4a2873c5acefbd3dbb@chromium.org>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult