Bluetooth - device discovery test on OS X

Print a debug message with an exact error code if device inquiry fails to start/fails -
otherwise it can be converted into UnknownError, which does not help if tests are failing.

-Make it even more verbose

Change-Id: I2b3de396de071757022274563d4f60d3064a0228
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>