setup.cfg: black and flake8 agree on error W504 (#525)

* setup.cfg: black and flake8 agree on error W504

* test_multiline_statement.py: flake8: noqa

* test_multiline_statement.py: flake8: noqa

* Update setup.cfg

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

* Update nose2/tests/functional/support/scenario/pretty_asserts/multiline_statement/test_multiline_statement.py

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

* max-complexity = 10

* flake8 --ignore=E203,W503 --max-complexity=17

* flake8: noqa

* extend-ignore = E203

* Update test_multiline_statement.py

* Comment out flake8 max-complexity setting

This value appears to have been reached experimentally, so we should
preserve the learned value.

But it hasn't been discussed/evaluated against the nose2 codebase, and
needs some thought before it can be included. In order to unblock
other config changes, comment it out and move it to the bottom of the
flake8 config.

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>
Co-authored-by: Stephen Rosen <sirosen@globus.org>

setup.cfg

@@ -6,11 +6,13 @@ profile = black
 known_third_party=six,coverage,mock
 
 [flake8]  # black and isort compatible rules
+extend-ignore = E203
 max-line-length = 88
-ignore = W503,W504,E203
 per-file-ignores =
     # allow use of `assert False` in tests -- it's fine
     nose2/tests/*.py:B011
     # FIXME: resolving these could change behavior -- do it in a separate
     #        cleanup and note it in the changelog
     nose2/plugins/loader/*.py:B004
+# proposed, but not yet accepted: max-complexity
+# max-complexity = 17