Escape terminal escape sequences in output with test failures

[blueyed]

Given t.py:

def test_foo():
    haystack = "= \x1b[33m\x1b[1m1 skipped\x1b[0m\x1b[33m in"
    assert "skipped" not in haystack

Running pytest t.py:

>       assert "skipped" not in haystack
E       AssertionError: assert 'skipped' not in '= \x1b[33m\...m\x1b[33m in'
E         'skipped' is contained here:
E           = 1 skipped in
E         ?              +++++++

The "1 skipped in" is colored there.

This also applies to \r etc.

It is the reason for output like:

>       assert "1 passed in" in rest
\n'

(https://travis-ci.org/pytest-dev/pytest/jobs/516821221#L784)

I think it would be good to escape special characters sequences here. Likely \x1b, \r, \n, \r might be enough?