Add livetests for 2.13.11
Add livetests for 2.13.11

Add 2.13.11 to the test parameterization and make adjustments:

- Releases prior to 2.14 are on dockerhub under the "gerritforge"
namespace rather than "gerritcodereview", so refactor GerritContainer
to use the correct image name.

- Releases prior to 2.14 still used digest authentication rather
  than basic.

- The docker images for releases prior to 2.14 do not include the
  plugin manager that overrides the first GET request. Calling GET
  on an empty endpoint with 2.13.x results in a 404, so change the
  dummy GET to use an actual endpoint.

Change-Id: Iccad17d4f46aefe11588e7e18b9b07a072d23ff3

dpursehouse/pygerrit2