Disable notifications while running unit tests

Summary:
Currently, we'll try to publish notifications while running tests. This is at best unnecessary and at worst problematic (we don't stub out the server).

For now, just never publish them.

Test Plan: Ran unit tests with notifications enabled but the server down and didn't get a bunch of warnings.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D10171