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

tests/unit/test_stubs.py

@@ -1,6 +1,8 @@
 from vcr.stubs import VCRHTTPSConnection
 
+
 class TestVCRConnection(object):
+
     def test_setting_of_attributes_get_propogated_to_real_connection(self):
         vcr_connection = VCRHTTPSConnection('www.examplehost.com')
         vcr_connection.ssl_version = 'example_ssl_version'