[gantry][tests] Handler warning better from docker command. Do not us… #850

Job	Run time
Test container	3m 17s
shellcheck	9s
Test scripts (gantry_cleanup_images_spec.sh)	57s
Test scripts (gantry_common_options_spec.sh)	1m 12s
Test scripts (gantry_filters_spec.sh)	55s
Test scripts (gantry_jobs_spec.sh)	40s
Test scripts (gantry_login_docker_config_spec.sh)	51s
Test scripts (gantry_login_negative_spec.sh)	58s
Test scripts (gantry_login_spec.sh)	1m 7s
Test scripts (gantry_manifest_spec.sh)	53s
Test scripts (gantry_notify_spec.sh)	1m 13s
Test scripts (gantry_parallel_spec.sh)	1m 7s
Test scripts (gantry_rollback_spec.sh)	45s
Test scripts (gantry_service_multiple_spec.sh)	36s
Test scripts (gantry_service_no_running_tasks_spec.sh)	50s
Test scripts (gantry_service_single_spec.sh)	55s
Test scripts (gantry_update_options_spec.sh)	48s
Build and push Docker image	1m 3s
	18m 16s

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