When cancelling addition of an Almanac interface, return to the Device page

Summary:
Fixes T13184. In Almanac, interfaces are always added to devices. However, if you "Add New Interface" and then "Cancel", you go to the nonexistent /interface/ page.

Instead, return to the device page.

Test Plan: From a device page, clicked "Add Interface" and then "Cancel". Ended up back where I was.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13184

Differential Revision: https://secure.phabricator.com/D19573