Move mBluetoothService.runBluetooth after broadcasting the STATE_ON intent.

This is because broadcastState method move the Bluetooth adapter state
to ON. The mBluetoothService.runBluetooth should be called only in the ON state.
Remove mIsDiscovering variable in BluetoothService.
Fix a bug in BluetoothA2dpService that caused 2 times of state change
from DISCONNECTED to CONNECTING that messed up BluetoothService's
connection state count.
Change-Id: Ifb782a845ae70f007d2e036d930bb55f445d68b5