Update operation time reported to service control (envoyproxy#207)

Do not use request start time as the operation start time when reporting
the operation to service control. Service control requires the operation
time to be recent (on the order of seconds). Given that a request can
have arbitrary latency, the start time of the request might be arbitrarily
old.

contrib/endpoints/src/api_manager/service_control/proto.cc

@@ -803,7 +803,7 @@ void SetOperationCommonFields(const OperationInfo& info,
     op->set_consumer_id(std::string(kConsumerIdApiKey) +
                         std::string(info.api_key));
   }
-  *op->mutable_start_time() = CreateTimestamp(info.request_start_time);
+  *op->mutable_start_time() = current_time;
   *op->mutable_end_time() = current_time;
 }