catch exception raised if url is not reachable

lib/exchange_rate.py

@@ -28,8 +28,11 @@ class Exchanger(threading.Thread):
         self.discovery()
 
     def discovery(self):
+        try:
             connection = httplib.HTTPSConnection('blockchain.info')
             connection.request("GET", "/ticker")
+        except:
+            return
         response = connection.getresponse()
         if response.reason == httplib.responses[httplib.NOT_FOUND]:
             return