Use the correct registry_uri to check if we need to sudo

[jfongatyelp]

In #3728 we changed the --docker_registry's default value from our DEFAULT_SPARK_DOCKER_REGISTRY and instead leave it undefined by default.

However, we still used args.docker_registry in our check whehter we needed sudo to push ot this registry, rather than using the generated registry_uri, which caused all runs with --build to try to sudo to push the registry, which doesn't work w/ the default registry.

This fixes to use our new registry_uri which should be either the requested docker_registry or the service's default, to get back to the normal behavior.

[nemacysts]

i am dumb, sorry ;_;