cloudinit: remove global disable of pylint W0107 and fix errors

[OddBloke]

This includes removing a test class which contained no tests but wasn't
detected as empty because of an errant pass statement.

(Also update the comment in .pylintrc to match what we actually filter.)

[igalic]

🙋🏻‍♀️

[igalic]

i understand how the abstract methods don't need pass, but i'm surprised regular methods don't need it either

[OddBloke]

The docstring is part of the body of the method; the pass is extraneous. Given these two definitions:

def before():
  """docstring"""
  pass


def after():
  """docstring"""

we can use Python's ast module to examine them (though note that as the parser operates on strings, before and after here are actually strings containing the above definitions):

>>> ast.dump(ast.parse(before))                                                                                                                                                                                                                                                      
"Module(body=[FunctionDef(name='flush', args=arguments(posonlyargs=[], args=[], vararg=None, kwonlyargs=[], kw_defaults=[], kwarg=None, defaults=[]), body=[Expr(value=Constant(value='docstring', kind=None)), Pass()], decorator_list=[], returns=None, type_comment=None)], type_ignores=[])"
>>> ast.dump(ast.parse(after))
"Module(body=[FunctionDef(name='after', args=arguments(posonlyargs=[], args=[], vararg=None, kwonlyargs=[], kw_defaults=[], kwarg=None, defaults=[]), body=[Expr(value=Constant(value='docstring', kind=None))], decorator_list=[], returns=None, type_comment=None)], type_ignores=[])"

The key differences here are the body of the FunctionDef. For before, it's two statements: [Expr(value=Constant(value='docstring', kind=None)), Pass()], whereas for after it is just a single one: [Expr(value=Constant(value='docstring', kind=None))]

[OddBloke]

(Also, plugging the definitions into https://vpyast.appspot.com/ will give you a nice graphical indicator of this.)