[gantry] follow the image remover's log and eval_cmd stdout. #725

Job	Run time
shellcheck	7s
Test script (gantry_cleanup_images_spec.sh)	1m 5s
Test script (gantry_common_options_spec.sh)	1m 3s
Test script (gantry_filters_spec.sh)	45s
Test script (gantry_jobs_spec.sh)	40s
Test script (gantry_login_docker_config_spec.sh)	57s
Test script (gantry_login_negative_spec.sh)	1m 8s
Test script (gantry_login_spec.sh)	1m 15s
Test script (gantry_manifest_spec.sh)	56s
Test script (gantry_notify_spec.sh)	1m 9s
Test script (gantry_parallel_spec.sh)	1m 2s
Test script (gantry_rollback_spec.sh)	49s
Test script (gantry_service_multiple_spec.sh)	29s
Test script (gantry_service_no_running_tasks_spec.sh)	53s
Test script (gantry_service_single_spec.sh)	46s
Test script (gantry_update_options_spec.sh)	52s
Build and push Docker image	1s
Test container	1s
	13m 58s

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