Set actions queue label from config.cfg.

Summary:
YOU MUST RERUN ./setup.sh AFTER THIS COMMIT.

The main point here is to allow the unit tests in test_actions.py to pass if
another Inbox instance is running concurrently. Previously, that instance would
grab actions enqueued by the test, causing the test to fail.

Another solution would be to use a separate Redis instance for the tests, but
that seems a lot more complicated.

Test Plan: Ran ./runtests with ./inbox debug running in the background.

Reviewers: spang, mg

Reviewed By: spang

Differential Revision: https://review.inboxapp.com/D21