swift234

[Python] Ignore some newly introduced flake8 rules we do not comply with

Disable:
* E114 indentation is not a multiple of four (comment)
* E266 too many leading '#' for block comment
* E402 module level import not at top of file

After this commit:

```
$ flake8
$
```

Fixing "indentation is not a multiple of four (comment)" is doable
but would mess up `git blame` for a handful of Python files. Perhaps
worth it?

Fixing "too many leading '#' for block comment" would require changing
the file header format used for Python files in the Swift repo.

Fixing "module level import not at top of file" would require taking
care of some `sys.path.append(…)` magic.