When --ne/--no-emails is added to 'repo upload' command line, gerrit
server will not generate notification emails.
project.py:Project.UploadForReview method is modified to accept a
string recognizable by gerrit to indicate different sets of destination
email addressees, but the upload command line allows only one option -
disable sending emails completely.
Default repo upload behavior is not being changed.
TEST=tried in the Chrome OS repo, observed that patches uploaded with
--ne or --no-emails indeed do not trigger any emails, while
patches uploaded without these command line options still trigger
email notifications.
Change-Id: I0301edec984907aedac277d883bd0e6d3099aedc