[Bluetooth] remove 'isConnected' in BluetoothSocket object

BluetoothSocket object doesn't have 'isConnected' property, and
this fix just concerns Bluez 4 backend.
[Bluetooth] add adapter.sockets.push when calling connectToServiceByUUID API

Socket should be stored in adapter object after creation

concerns TCT test cases :
- BluetoothSocket_onmessage_callback
- BluetoothSocket_readData
Merge pull request #374 from Pating/master

two bluetooth bugs