fromupstream: Support multiple bug lines

If we add multiple -b params to the command only one is processed.

We also take this chance to unify the way we handle the bugs

BUG=None
TEST=fromupstream.py upstream://abcde --test="None" --bug="b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123, b:123" --crbug=56 --crbug=67

Change-Id: I4f453e050d8b14a485eea40b7ae2ff1418bafd00
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2629555
Tested-by: Ricardo Ribalda <ribalda@chromium.org>
Commit-Queue: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Auto-Submit: Ricardo Ribalda <ribalda@chromium.org>
1 file changed