change Analytics backend service.

- The `split` method has been added to correctly extract the aggregation method name from the dictionary.

src/analytics/backend/service/AnalyticsBackendService.py

@@ -42,7 +42,7 @@ class AnalyticsBackendService(GenericGrpcService):
 
     def StartSparkStreamer(self, analyzer_uuid, analyzer):
         kpi_list      = analyzer['input_kpis'] 
-        oper_list     = [s.replace('_value', '') for s in list(analyzer["thresholds"].keys())]  # TODO: update this line...
+        oper_list     = [s.split('_', 1)[0] for s in list(analyzer["thresholds"].keys())]  # TODO: update this line...
         thresholds    = analyzer['thresholds']
         window_size   = analyzer['window_size']
         window_slider = analyzer['window_slider']