While fetching monorail issues, @chromium.org is appended to the --user
option even if the original --user option is already a email address
(e.g. user@google.com).

Change-Id: I2442f4ea977b2681a72271f7c20fabb1ceaa351c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1790222Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
Commit-Queue: Peter Lee <pkl@chromium.org>