native: support postPersist method

It should be called for NEO contract to distribute
committee bounties.

pkg/rpc/server/subscription_test.go

@@ -120,6 +120,13 @@ func TestSubscriptions(t *testing.T) {
 			}
 		}
 		resp = getNotification(t, respMsgs)
+		require.Equal(t, response.ExecutionEventID, resp.Event)
+		for {
+			resp = getNotification(t, respMsgs)
+			if resp.Event != response.NotificationEventID {
+				break
+			}
+		}
 		require.Equal(t, response.BlockEventID, resp.Event)
 	}