Option to disable progress spinner

I am using `gsutil` in a scripting environment to move large files. I need to have progress logged so we can monitor jobs and get status updates. However, the progress indicator for `gsutil cp` includes a spinner that assumes it is working in a terminal. This produces an incredible amount of garbage in a log file.

This is related to #429 and #265 but is not the same request. I still need to see the progress, it just needs to omit the special control characters that assume the output is a terminal window. In other words, I want an option to remove the spinner and instead just write a new line.