Cache http client with private SD

scripts-available/CDB_Groups_API.sql

@@ -115,7 +115,7 @@ $$
     last_err = None
     while retry > 0:
       try:
-        client = GD['groups_api_client'] = httplib.HTTPConnection(params['host'], params['port'], False, params['timeout'])
+        client = SD['groups_api_client'] = httplib.HTTPConnection(params['host'], params['port'], False, params['timeout'])
         client.request(method, url, body, headers)
         response = client.getresponse()
         assert response.status in [ 200, 409 ]
@@ -124,7 +124,7 @@ $$
         retry -= 1
         last_err = err
         plpy.warning('Retrying after: ' + str(err))
-        client = GD['groups_api_client'] = None
+        client = SD['groups_api_client'] = None
 
     if last_err is not None:
       plpy.error('Fatal Group API error: ' + str(last_err))