The email address used for notification on try was templated,
but nothing actually evaluated the template. This applies the same
templating that applies to the message to any emails specified.
Differential Revision: https://phabricator.services.mozilla.com/D1297
Sends 'in the candidates directory', 'pushed to cdntest', etc emails only when the underlying dummy tasks succeed, avoiding false messages when graphs are cancelled or the dummy job fails for infrastructure reasons.
Also sets the body of the email to be the same string as the subject, as we used to do, to avoid unnecessary information about the dummy task.
