Align git-review and python -m git_review.cmd behaviors

Currently, python -m git_review.cmd wraps git_review.cmd.main call to
handle correctly unicode in python2 where git-review calls directly
git_review.cmd.main. This change embeds the wrapper inside main in
order to align git-review and python -m git_review.cmd behaviors.

Change-Id: I390e2d68b851299c3b07292b89dee8198068e6aa
Merge "Align git-review and python -m git_review.cmd behaviors"