Fix a race condition and possible deadlock when changing BT status.

We have to make sure to synchronize when changing either the BT
connection status or the "running" state of the BT data source.
Work in progress for thread safety in BT source.
Take a more explicit approach to thread safety in BT vehicle interface.
Add missing import.
Don't block the UI waiting to stop the BT data source.
Quickly and forcefully stop the Bluetooth connection setup.