User could attach CC addresses to the gerrit change created.

BUG=1294382
TEST=train

Change-Id: I236658d80f41b27bf007bb344934ce835cd7b5de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3440862Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Xinan Lin <linxinan@chromium.org>