maint: Use flake8 to check python code

maint: Use flake8 to check python code

Replace 'sc_prohibit_semicolon_at_eol_in_python' with generic 'sc_flake8' rule
to check python code style.

Now 'sc_flake8' just check the error E703: 'statement ends with a semicolon'.
In future, we could use '--select' to introduce more rules.

Signed-off-by: Shi Lei <shi_lei@massclouds.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Ján Tomko <jtomko@redhat.com>