Make Bluetooth adapter choosable for device and service search

In case there are more Bluetooth adapter, device and service search
might give different results.

Addition to Change-Id: Ideddb39460985c18547baec986b15e43946c85de - added option
for setting the device adapter for service search. QBluetoothLocalDevice was used
in both classes (device and service search) for passing an argument for setting
adapter. The reason for this to keep the same approach, because in
QBluetoothServiceDiscoveryAgent class there is already a constructor
with QBluetoothAddress argument.

Auto tests and examples updated.

Change-Id: Ib5d7ff23e4846d9d42dae68d8d424031748811e5
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>