Add unique constraint to AlmanacInterfaces

Summary: See discussion in D19379. The 4-tuple of (device, network, address, port) should be unique.

Test Plan: Created lots of duplicate interfaces, bound those interfaces to various services, observed migration script clean things up correctly.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, PHID-OPKG-gm6ozazyms6q6i22gyam

Differential Revision: https://secure.phabricator.com/D19388