Add Bluetooth enable

Add Bluetooth enable

Use the network API interface object to enable Bluetooth via ConnMan,
thus deactivating the default rfkill state and persisting the new one
across reboots (since ConnMan will restore the enabled state on boot).
This used to be done in the agl-service-bluetooth binding, doing it
here should be considered a likely temporary placeholder for further
investigation into Bluetooth device management in future AGL releases.

At the moment device auto-connection is not likely to match pre-Marlin
releases unless a device manages to connect on its own versus the
active auto-connect that was in agl-service-bluetooth.  The latter is
now dependent on this application being run until further
re-architecting takes place.

Bug-AGL: SPEC-4253

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Ic18452a65345da82a27370a46fbc7121cbf85aea