Update tests to use Gerrit 2.9.2

Gerrit 2.9 adds the '--all-reviewers' option to 'gerrit query', which
allows testing that reviewers have been successfully added to a patch
set in tests for new reviewer functionality.

Change-Id: I17f37c8fd46578b4a8cbfacee4eb8073972b2eee
Merge "Update tests to use Gerrit 2.9.2"