Fix run_interop_tests override_server option

tools/run_tests/run_interop_tests.py

@@ -465,6 +465,7 @@ def cloud_to_prod_jobspec(language, test_case, server_host_name,
           flake_retries=5 if args.allow_flakes else 0,
           timeout_retries=2 if args.allow_flakes else 0,
           kill_handler=_job_kill_handler)
+  if docker_image:
     test_job.container_name = container_name
   return test_job
 
@@ -501,6 +502,7 @@ def cloud_to_cloud_jobspec(language, test_case, server_name, server_host,
           flake_retries=5 if args.allow_flakes else 0,
           timeout_retries=2 if args.allow_flakes else 0,
           kill_handler=_job_kill_handler)
+  if docker_image:
     test_job.container_name = container_name
   return test_job