R1:285cb172e962

Try literal search if operator search fails in elasticsearch

Test Plan: Searched for `[test]` in /search/ and in revision dependencies.

Reviewers: epriestley

Reviewed By: epriestley

CC: tbrzezinsky, aran, Korvin

Maniphest Tasks: T1757

Differential Revision: https://secure.phabricator.com/D3427