Allow serialization impl to be overridden

Change-Id: I0f955c78897d4212f06942e59a7018dbe5d28540

keystoneclient/client.py

@@ -107,6 +107,9 @@ class HTTPClient(httplib2.Http):
         if self.debug_log:
             _logger.debug("RESP: %s\nRESP BODY: %s\n", resp, body)
 
+    def serialize(self, entity):
+        return json.dumps(entity)
+
     def request(self, url, method, **kwargs):
         """ Send an http request with the specified characteristics.
 
@@ -119,7 +122,7 @@ class HTTPClient(httplib2.Http):
         request_kwargs['headers']['User-Agent'] = self.USER_AGENT
         if 'body' in kwargs:
             request_kwargs['headers']['Content-Type'] = 'application/json'
-            request_kwargs['body'] = json.dumps(kwargs['body'])
+            request_kwargs['body'] = self.serialize(kwargs['body'])
 
         self.http_log_req((url, method,), request_kwargs)
         resp, body = super(HTTPClient, self).request(url,