Use the lower-level set_default API so I can intersperse the hipchat messages.

Summary:
This allows me to easily add in two messages -- one html format and
one not -- which would have been difficult before, when I would have
had to use the --hipchat-message flag to set_default.py

Test Plan: Will test when I deploy next!

Reviewers: benkomalo

Differential Revision: http://phabricator.khanacademy.org/D13785