Fix pyflakes and pep8 errors

Use extra asserts to use previously unused variables in tests,
such as `cass` and `response`.

Fix only pyflakes errors in docs/conf.py

vcr/util.py

@@ -71,6 +71,7 @@ class CaseInsensitiveDict(collections.MutableMapping):
     def __repr__(self):
         return str(dict(self.items()))
 
+
 def partition_dict(predicate, dictionary):
     true_dict = {}
     false_dict = {}
@@ -89,6 +90,7 @@ def compose(*functions):
         return res
     return composed
 
+
 def read_body(request):
     if hasattr(request.body, 'read'):
         return request.body.read()