[Python] Improve model equality implementation (#4663)

* [Python] Improve model equality implementation

The model equality implementation template blindly tried accessing the
`__dict__` attribute of the variable to compare equality against. This
attribute does not exist for a lot of Python built-in types (`None`,
`str` etc.) and the equality check would simply crash.

This adds a simple guard to only continue with equality check if the
variable to compare is an instance of the model being compared against.

* Remove wrong auto-update of Python requirements

samples/client/petstore-security-test/python/petstore_api/api_client.py

@@ -116,7 +116,7 @@ class ApiClient(object):
                                                     collection_formats)
             for k, v in path_params:
                 resource_path = resource_path.replace(
-                    '{%s}' % k, quote(str(v)))
+                    '{%s}' % k, quote(str(v), safe=""))
 
         # query parameters
         if query_params:

samples/client/petstore-security-test/python/petstore_api/apis/fake_api.py

@@ -116,12 +116,9 @@ class FakeApi(object):
             form_params.append(('test code inject */ ' " =end -- \r\n \n \r', params['test_code_inject____end____rn_n_r']))
 
         body_params = None
-
         # HTTP header `Accept`
         header_params['Accept'] = self.api_client.\
             select_header_accept(['application/json', '*/  \" =end --       '])
-        if not header_params['Accept']:
-            del header_params['Accept']
 
         # HTTP header `Content-Type`
         header_params['Content-Type'] = self.api_client.\

samples/client/petstore-security-test/python/petstore_api/models/model_return.py

@@ -105,6 +105,9 @@ class ModelReturn(object):
         """
         Returns true if both objects are equal
         """
+        if not isinstance(other, ModelReturn):
+            return False
+
         return self.__dict__ == other.__dict__
 
     def __ne__(self, other):