Add bu and BackupRestoreConfirmation to the core build

The 'bu' program is used by the platform's local backup mechanism
to stream a 'tar'-compatible dump of application packages/data.

BackupRestoreConfirmation is the UI for verifying that the user
did is aware of & grants permission for a requested full backup or
restore operation.

Change-Id: I3a3fe345e89d09838bddc4010d429e1374e19440