Implement switchConnectable with Powered property setting instead of scan modes

Bluez powered property setting is more apropriate for what this method intend to
achieve and it fixes a bug that incoming connection request wake up the stack in
The pairable events are replaced by power and discoverable events
HotOff state
bug 5080232

Change-Id: I43b44cb2f5203bd99bf764d5a1696e8ff52a31db