Support standard deviation and json output for job stats

In the job stats, in addition to the max, min and average,
it will also display the standard deviation.

A new option --json is added to the rdci to output the results
in json format.

In the job stats, using the GMT time instead of timestamp
for start and end time.

Change-Id: If245c4fc4854a1dc867f97ff5aa9112af7962eca

server/src/rdc_server_main.cc

@@ -312,6 +312,12 @@ RDCServer::ShutDown(void) {
     delete rdc_admin_service_;
     rdc_admin_service_ = nullptr;
   }
+
+  if (api_service_) {
+    delete api_service_;
+    api_service_ = nullptr;
+  }
+
 }
 
 static void * ProcessSignalLoop(void *server_ptr) {