Add an explicit "uri" to the "harbormaster.buildable.search" results

Summary: Ref T13546. This makes some "arc" tasks a little easier, and will make them more correct if "arc" ever switches to using SSH.

Test Plan: Ran "harbormaster.buildable.search" from the web UI, saw URIs in the result set.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13546

Differential Revision: https://secure.phabricator.com/D21346