Crash in Settings observed while changing the device orientation after renamed tablet

There was a fundamental flow in the BT code. Basically BluetoothSettings is using
a singleton BluetoothDiscoverableEnabler.

BluetoothDiscoverableEnabler is keeping (thru its constructor) a reference on a Context
for registering/unregistering some broadcast receiver. BUMMER! When you change orientation
(or more generally the device Configuration), your Context is no more the same!

Hence the crash as we were  trying to unregister a Receiver on a Context that is no more valid.

Fix that issue by passing an updated Context to the BluetoothDiscoverableEnabler.resume() API.

Bug #12991455
Change-Id: I77db15d2b59b6dd973907e26f9e6bb022202a8b5