[tests] add a check_timeout function. #907

Job	Run time
Test container	2m 58s
Test scripts (gantry_cleanup_images_spec.sh)	1m 1s
shellcheck	11s
Test scripts (gantry_common_options_spec.sh)	1m 14s
Test scripts (gantry_filters_spec.sh)	51s
Test scripts (gantry_jobs_spec.sh)	53s
Test scripts (gantry_login_docker_config_spec.sh)	58s
Test scripts (gantry_login_negative_spec.sh)	1m 14s
Test scripts (gantry_login_spec.sh)	1m 6s
Test scripts (gantry_manifest_spec.sh)	1m 1s
Test scripts (gantry_notify_spec.sh)	1m 17s
Test scripts (gantry_parallel_spec.sh)	1m 0s
Test scripts (gantry_rollback_spec.sh)	47s
Test scripts (gantry_service_multiple_spec.sh)	33s
Test scripts (gantry_service_no_running_tasks_spec.sh)	53s
Test scripts (gantry_service_single_spec.sh)	56s
Test scripts (gantry_update_options_spec.sh)	1m 1s
Build and push Docker image	1m 1s
	18m 55s

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