Changed an assert to more specific assert method

Following OpenStack Style Guidelines [1], I changed:
assertFalse(sth in sth) to assertNotIn(sth, sth).

After this change, a more specific message is shown on error.

[1]: http://docs.openstack.org/developer/hacking/#unit-tests-and-assertraises

Change-Id: I929900eb5dc48eb04b541e387b70d69c4865ca03

ironic_inspector/test/unit/test_plugins_extra_hardware.py

@@ -75,7 +75,7 @@ class TestExtraHardware(test_base.NodeTest):
             [{'op': 'add', 'path': '/extra/hardware_swift_object',
               'value': name}])
 
-        self.assertFalse('data' in introspection_data)
+        self.assertNotIn('data', introspection_data)
 
     def test_no_data_recieved(self, patch_mock, swift_mock):
         introspection_data = {'cats': 'meow'}