Fix bug 2619062 Music is routed to Phone speaker, though it is

connected to A2DP media profile

When the phone is docked and using the dock A2DP, and the user
connects another A2DP device, make the dock unavailable immediately
before connecting the new A2DP device.

Change-Id: I82d53836fb509ee4ea7cdb68f467dfb946c634f8