The current BugsFromDescription code returns ['1234, 5678'] but I think it
should return ['1234', '5678']. For 'BUG=1234, 5678' this already works.

This was preventing me from uploading
https://chromium-review.googlesource.com/c/catapult/+/1481239
because of https://cs.chromium.org/chromium/src/third_party/catapult/PRESUBMIT.py?q=catapult/PRESUBMIT.py&sq=package:chromium&g=0&l=52

See https://logs.chromium.org/logs/catapult/buildbucket/cr-buildbucket.appspot.com/8920885706080647120/+/steps/presubmit/0/stdout

Change-Id: Ibb3fca8c7a6ec664cdf9a38a8a7ac2bf66cb73ed
Reviewed-on: https://chromium-review.googlesource.com/c/1481240
Auto-Submit: Caleb Rouleau <crouleau@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>