This is a revision of change If45290b87 with updated tests that no longer
need to take NoteDB into account separately.
The PostReview REST endpoint translates each new reviewer in the request
into invocations of the PostReviewers REST endpoint, which would send a
newchange email each time a reviewer is successfully added. Because the
PostReview endpoint allows several Reviewers and CC'd users in batch,
prevent the PostReviewers sub-calls from sending emails, and send one
newchange email at the end.
Tests are updated to reflect fewer emails being sent and to reflect CC'd
user names no-longer appearing in the email salutation.
Bug: Issue 4563
Change-Id: I1cfd56ac1a2d107b9f6aae58ed056a1a458410af
92cba85254