[autotest] switch to use monorail for bug filing

Soon we will switch from bug tracker to monorail to file bugs. Change
the bug filing code to switch the credentials. And also choose the
proper server for different purpose (prod or testing).

BUG=None
TEST=File bug locally with the new credentials

Change-Id: I12a88dc70113ab782d70602524dbce226eec564a
Reviewed-on: https://chromium-review.googlesource.com/328002
Commit-Ready: Shuqian Zhao <shuqianz@chromium.org>
Tested-by: Shuqian Zhao <shuqianz@chromium.org>
Reviewed-by: Fang Deng <fdeng@chromium.org>
diff --git a/global_config.ini b/global_config.ini
index 5d609e7..08cf065 100644
--- a/global_config.ini
+++ b/global_config.ini
@@ -336,6 +336,7 @@
 gs_file_prefix: gs://
 chromium_email_address = @chromium.org
 credentials: USE SHADOW CREDENTIALS
+monorail_server:
 client_id: USE SHADOW CLIENT_ID
 client_secret: USE SHADOW CLIENT_SECRET
 scope: USE SHADOW SCOPE