Home default setting should not shown in managed profile settings

Each default preference needs to have its corresponding
PreferenceAvailabilityProvider to provide us the availability of it.
If no corresponding provider is found, it is considered to be not
available. So it encourages other developers who will add new default app
preference later to consider the availability of it.

Bug:27143673
Change-Id: I073b7122dddc579504f397c5de2bdd4df3826269