Fix F901 errors and disable W504 checks
The following error is fixed:
F901 'raise NotImplemented' should be 'raise NotImplementedError'
The following error is now ignored:
W504 line break after binary operator
It is ignored because moving the line break to before the binary operator
causes W503 error (line break before binary operator). With this change
we get closer to consistency throughout the project.
Signed-off-by: Luiz Carvalho <lucarval@redhat.com>