[bind10-dev] Minor change to Python style guidelines

[zhanglikun]

> Our "official" Python style guidelines are basically just to use the
> Python style guidelines:
> 
> https://bind10.isc.org/wiki/CodingGuidelines
> 
> Jelte suggested that it might be nice to put the __init__() function as
> the first method in a class. I didn't see anything in the Python style
> about this, but I am not opposed to it.
> 
> Shall I add this as an extra guideline to our Python style?
> 
Agree, 

BTW, I checked my python code and found __init__() always be the first
function in the class, except the __init__() in child classes without
explicitly provided.

Zhang Likun