title: Scaning BLE device by CBUUID doesn't work
body: <p>I'm trying to scan for a specific BLE Device on my app by specifying a CBUUID in the <code>scanForPeripheralsWithServices()</code>, but if I mention it scan is never processed.</p>
  
  <p>Here is my <code>CBCentralManagerDelegate</code> code:</p>
  
  <pre><code>func centralManagerDidUpdateState(central: CBCentralManager) {
      switch (central.state) {
      case CBCentralManagerState.PoweredOff:
          print("BLE powered off")
          self.clearDevices()
  
      case CBCentralManagerState.Unauthorized:
          // Indicate to user that the iOS device does not support BLE.
          print("BLE not supported")
          break
  
      case CBCentralManagerState.Unknown:
          // Wait for another event
          print("BLE unknown event")
          break
  
      case CBCentralManagerState.PoweredOn:
          print("BLE powered on")
              self.startScanning()
          break
  
      case CBCentralManagerState.Resetting:
          print("BLE reset")
          self.clearDevices()
  
      case CBCentralManagerState.Unsupported:
          print("BLE unsupported event")
          break
      }
  }
  
  
      func startScanning() {
      print("\(NSDate()) Start scanning...")
         if let central = centralManager {
          let dictionaryOfOptions = [CBCentralManagerScanOptionAllowDuplicatesKey : true]
          let ble = [CBUUID(string: "B737D0FF-AF53-9B83-E5D2-922140A9FFFF")]
          central.scanForPeripheralsWithServices(ble, options: nil)
          }
  }
  
  
  
    func centralManager(central: CBCentralManager, didDiscoverPeripheral peripheral: CBPeripheral, advertisementData: [String : AnyObject], RSSI: NSNumber) {
      print("Discovered peripheral \(RSSI) dBM name: \(peripheral.name)")
      print("UUID: \(peripheral.identifier.UUIDString)")
      print("Peripheral \(peripheral.identifier)")
      .....send event to server....   
      sleep(delayPolling)
      self.startScanning()
  
  }
  </code></pre>
  
  <p>If I change the <code>scanForPeripheralsWithServices()</code> without any CBUUID String it works fine:</p>
  
  <pre><code>central.scanForPeripheralsWithServices(nil, options: dictionaryOfOptions)
  </code></pre>
  
  <p>My main concern if to be able to launch this Thread in background and from Apple documentation, we need to scan for a specific device by specifying the CBUUID to be able to run my task.</p>
  
  <p>Can you tell me where I'm wrong?</p>