[tests] add a label to services, containers and images created for te… #911

Job	Run time
Test container	3m 9s
shellcheck	9s
Test scripts (gantry_cleanup_images_spec.sh)	1m 1s
Test scripts (gantry_common_options_spec.sh)	1m 8s
Test scripts (gantry_filters_spec.sh)	59s
Test scripts (gantry_jobs_spec.sh)	41s
Test scripts (gantry_login_docker_config_spec.sh)	54s
Test scripts (gantry_login_negative_spec.sh)	1m 3s
Test scripts (gantry_login_spec.sh)	1m 12s
Test scripts (gantry_manifest_spec.sh)	1m 3s
Test scripts (gantry_notify_spec.sh)	1m 22s
Test scripts (gantry_parallel_spec.sh)	1m 0s
Test scripts (gantry_rollback_spec.sh)	58s
Test scripts (gantry_service_multiple_spec.sh)	33s
Test scripts (gantry_service_no_running_tasks_spec.sh)	54s
Test scripts (gantry_service_single_spec.sh)	59s
Test scripts (gantry_update_options_spec.sh)	1m 5s
Build and push Docker image	1m 16s
	19m 26s

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