Fix async reserved word in python3.7

kubernetes-client has patched this [1]. To retain backwards
compatibility, we can use **kwargs to handle async/async_req arguments

[1]: b10c7b6a17

Change-Id: I8e738b4f99091786dd76e081bffa36ef5ab70085

magnum/conductor/k8s_api.py

@@ -45,10 +45,10 @@ class ApiClient(api_client.ApiClient):
 
     def call_api(self, resource_path, method,
                  path_params=None, query_params=None, header_params=None,
-                 body=None, post_params=None, files=None, async=None,
-                 response_type=None, auth_settings=None, async_req=None,
+                 body=None, post_params=None, files=None,
+                 response_type=None, auth_settings=None,
                  _return_http_data_only=None, collection_formats=None,
-                 _preload_content=True, _request_timeout=None):
+                 _preload_content=True, _request_timeout=None, **kwargs):
         """Makes http request (synchronous) and return the deserialized data
 
         :param resource_path: Path to method endpoint.
@@ -64,8 +64,6 @@ class ApiClient(api_client.ApiClient):
         :param response: Response data type.
         :param files dict: key -> filename, value -> filepath,
             for `multipart/form-data`.
-        :param async bool: to be compatible with k8s-client before 7.0.0
-        :param async_req bool: execute request asynchronously
         :param _return_http_data_only: response data without head status code
                                        and headers
         :param collection_formats: dict of collection formats for path, query,