Fix pep8, coding, unsed import and operator "is" 

Hi @tarruda 

I fix some issue to be compliant with PEP8 and Flake8 tools, see:
```
remove unused import
fix local import with "from . import" syntax
To compare with None, only use "is" operator
Add coding at the beginning of each files
```

Travis-ci test is ok with flake8 verification.

Regards,
Are you sure `sleep` wasn't imported for the user of the client? If you are, why comment the line instead of removing it?