SAP: Avoid having multiple active SapServers instances

It turns out that the shutdown procedure can take along time,
which causes the race between shutting down and freeing resources,
and accepting a new connect request.
This fix waits for the shutdown procedure complete before allowing
a new incomming connection.

Additionally handling of serivce shutdown while connected - e.g.
BT off is fixed.

Messaghandler changed to use it's own thread, as during shutdown
the default messagehandler occationally stops handling messages.
By using a looper from a HandlerThread instance, this issue no
longer exists.

Change-Id: Ife71a06b4e481fb61ca8c6189d43c3cd3c630da0