Use -l parameter of su in upstart jobs.

Summary:
This makes the environment (i.e. PATH) more like what you'd expect if you were
logged in as ci.

Apparently mr-deploy-daemon relies on PATH to find the GAE SDK.

Test Plan: on ka-ci

Reviewers: alpert, dylan

Reviewed By: alpert

CC: stephanie, csilvers

Differential Revision: http://phabricator.khanacademy.org/D2064