We have had a couple issues with newer agents not working with old
servers or vice versa. Add a CI test to test variations on
uplevel/downlevel server/agent against latest, stable, and the previous
branch.
Signed-off-by: Brad Davidson <brad.davidson@rancher.com>
(cherry picked from commit 357c375d04737ed8300c9b5caaf25c7966a85013)