fix(controller): add south_migrations to flake8

Author: Matthew Fisher

setup.cfg

@@ -1,4 +1,4 @@
 [flake8]
 max-line-length = 99
-exclude = */api/migrations/*,*/build/*,*/venv/*,*/virtualenv/*,*/scheduler/*,*/templates/*
+exclude = */api/migrations/*,*/api/south_migrations/*,*/build/*,*/venv/*,*/virtualenv/*,*/scheduler/*,*/templates/*
 max-complexity = 12