Add flake8 config file for ignoring black styles linting error.

[RatanShreshtha]

Added .flake8 file copied mainly from https://github.com/theacodes/nox/blob/master/.flake8 and removed the # noqa.

[haikuginger]

Could you rebase this specific change on master rather than on the "remove addCleanup" branch? Thanks!

[RatanShreshtha]

I have updated the PR.

[sethmlarson]

Looks like black is catching a linting issue?

[codecov-io]

Codecov Report

Merging #1631 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1631      +/-   ##
==========================================
- Coverage   99.47%   99.47%   -0.01%     
==========================================
  Files          22       22              
  Lines        1915     1900      -15     
==========================================
- Hits         1905     1890      -15     
  Misses         10       10

Impacted Files	Coverage Δ
src/urllib3/connection.py	93.75% <ø> (-0.09%)	⬇️
src/urllib3/util/url.py	99.1% <100%> (-0.04%)	⬇️
src/urllib3/util/timeout.py	100% <0%> (ø)	⬆️
src/urllib3/response.py	100% <0%> (ø)	⬆️

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[pquentin]

Can we expand the configuration in setup.cfg instead of creating a new file?

[RatanShreshtha]

Updated the PR and added the flake8 ignore rules in setup.cfg

[sethmlarson]

Thanks for this! :)