Fix when search "storage", there are multiple results

root cause: if device doesn't have external storage,
StorageSettings will launch PrivateVolumeSettings and finish itself.
But we still index the preferences in StorageSettings.

Solution: Check if device doesn't support external storage,
add all of StorageSettings preference into nonIndexableKey list.

Bug: 152366015
Test: robotest & manual

Change-Id: Ib559db3455d46a343ad7eb73e54eb72d0e833308