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>