Run isort and black

[gabor-boros]

Reason for the change
Before we are going further with preparing PY3 changes and shaping up the driver, it would be great to make sure we reduce the scope of the PRs and we can easily read the code.

Description
Run isort and black on the repository with default config.

Code examples
N/A

Checklist
N/A

References

• https://pypi.org/project/isort/
• https://pypi.org/project/black/

[gabor-boros]

Here is an overview of what got changed by this pull request:

Issues
======
+ Solved 174
- Added 107
           

Coverage increased per file
===========================
+ rethinkdb/tornado_net/net_tornado.py  1
         

Coverage decreased per file
===========================
- rethinkdb/errors.py  -1
         

Clones added
============
- rethinkdb/ast.py  2
- rethinkdb/_export.py  1
- rethinkdb/_dump.py  1
         

See the complete overview on Codacy