Option to suppress output object listing

hi!

I'm using cwltool and i'm missing a feature to supress the listing of output products. When a pipeline has a lot of output products the console gets filled up with data which is quite pointless. I tried `--quiet` but that doesn't seem to do much.

thanks!

- [ ] add test for `--quiet` having no output to stderr

Start by tracing cwltool's --quiet option and where output products are listed on the console. Define the expected quiet behavior, then add the requested test to verify that --quiet produces no output on stderr.

Written by the indexing model from the issue text.