use go swarming client in trigger.py
use go swarming client in trigger.py

python client is being deprecated.

Tested by
$ python third_party/angle/scripts/trigger.py --shards=2 -p chromium.tests out/Release base_unittests Ubuntu none

Fixed: chromium:1047115
Change-Id: Id653e2b29e8bf02ab86eaa4c5c767d081fa29dbd
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2095654
Commit-Queue: Yuly Novikov <36f5580f63d0a3eacc17e89a61d11e2f646630d2@chromium.org>
Reviewed-by: Yuly Novikov <36f5580f63d0a3eacc17e89a61d11e2f646630d2@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle