Bluetooth: tester: Use bt enable cb to indicate cmd rsp success

This is needed especially for nble. If bluetooth is not enabled we
cannot send another commands to tester.

Change-Id: I17e639301bba6efd127f2c743b8942c1b493f9da
Signed-off-by: Grzegorz Kolodziejczyk <grzegorz.kolodziejczyk@tieto.com>