Please suppress ANSI colors and progress spinner when TERM=dumb

[mgedmin]

I'm often running things like tox -p auto -e py27,py35 -- testfile::test_function from Vim, using its builtin quickfix window to look at the errors. (I've a plugin that runs the test under cursor with a single keystroke, it's very convenient.)

This is what I see with tox 3.9.0:

...

It would be amazing if tox noticed that $TERM was set to dumb and did not output all these ^M^[s

[gaborbernat]

on TERM dumb we should use ascii frames here https://github.com/tox-dev/tox/blob/rewrite/src/tox/util/spinner.py#L65