When using git cl upload --message-file, the text editor prompts the
user to edit the description. This change suppresses the editor when
a message file is passed in.

Change-Id: Ifa568e155e72eeb49f55ded0ddac1b5a940687af
Bug:916230
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2643781Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>