The integration tests had previously used the environment variable
DOCKER_INDEX_URL but it was apparently removed several months ago.
Change the integration auth tests to specify the ServerAddress field
of the AuthConfig struct to use the staging deployment of the index.
Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)
Upstream-commit: c914abaf15634d8039927176dfc5ff3c765f30d0
Component: engine
