src: qofonomanager: connect modemAdded and modemRemoved to ofono

Libqofono doesn't connect modemAdded and modemremoved to ofono. We
need to connect onModemAdd and onModemRemove in the beginning of
modem using qofonomanager.

Signed-off-by: TengChou Yang <tyang@cercacor.com>
qofonomanager: Fixed the bug for modem list.

modem path was not removed after modem are actually been disabled.
with this change we can have the most updated modem list.

Signed-off-by: TengChou Yang <tyang@cercacor.com>