Set the broker AMQP exchange as durable

Summary:
The Nasqueron notifications center needs, as explained on T781,
to declare an exchange as durable to be compatible with the way
the broker container setup script configures the exchange.

Depends on D336. Fixes T781.

Test Plan: Fire a notification

Reviewers: dereckson

Maniphest Tasks: T781

Differential Revision: http://devcentral.nasqueron.org/D337