* Add method to convert the following state values to string
- BluetoothHeadset.STATE_DISCONNECTED
- BluetoothHeadset.STATE_CONNECTING
- BluetoothHeadset.STATE_CONNECTED
- BluetoothHeadset.STATE_DISCONNECTING
Test: make
Change-Id: Iaa5b6e35d3214ded8edbe29d626e0869651417d1