Add test plan to differential.revision.search
Summary: Ref T13151. Ref PHI622.
Test Plan: Loaded a revision in the Conduit UI; observed presence of testPlan field.
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: Korvin
Maniphest Tasks: T13151
Differential Revision: https://secure.phabricator.com/D19518