Check reachability of bridges found using http://www.meethue.com/api/nupnp

[twam]

If you unplug my SmartBridge it still get's found using the http://www.meethue.com/api/nupnp method. So the API should check the results got from http://www.meethue.com/api/nupnp for reachability before reporting them as found bridges.