Use updated backend naming for log fetching

Summary:
This patch should be committed and deployed once
http://phabricator.khanacademy.org/D3643 is live in production. Some logs may
be dropped during the naming switch, but this should be less than an hour of
logs and can be backfilled.

Test Plan: Fingers crossed.

Reviewers: csilvers

Reviewed By: csilvers

Differential Revision: http://phabricator.khanacademy.org/D3644