Demo app page cannot remove sensor items when the resources are removed from the resource server

[qiuzhong]

Test Environments:

• HW: Edison, Temperature sensor v1.2
• SW: Ostro image build#481, OIC resource server: temperature.js

  Steps to reproduce:

  1. The resource server creates an OIC temperature resource, launch the Smart Home Control app. Now the demo app can find the temperature sensor. Everything works fine.
  2. Then at some time, the resource server stops the resource, observe the the app page. The temperature sensor item is still present, though the spinner at the up-right corner is running.
  3. Switch pages between the Sensor and About tab of left side, the temperature sensor remains.

But if we push the app to background and resume it or relaunch the demo app, the page can clean up temperature sensor.