chore: send errors to stderr

[iffse]

Context.

framework_tool uses both stdout and stderr. But the former one is being overused, having most of the error messages which should be sent to stderr.

This PR only changed print statements which should go to stderr.

[JohnAZoidberg]

In general this is not a bad idea. But I wonder how you noticed it.
The commands don't really return machine readable output. We're you trying to separate stdout and stdin on purpose?