Implement example: functions_storage_system_test

[coryan]

Line numbers are approximate:

https://github.com/GoogleCloudPlatform/golang-samples/blob/master/functions/helloworld/hello_cloud_storage_system_test.go#L20-L105

https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/functions/helloworld/sample_storage_test_system.py#L15-L70