Enable H904 PEP8 check

Fixes all files with the PEP8 error:

   H904  Wrap long lines in parentheses instead of a backslash

and enables the PEP8 check in tox.ini.

Change-Id: Ie3314487a45d34f59304a5b24eef9488ca3ce35e
Merge "Enable H904 PEP8 check"