packaging: engine-backup: Refuse restoring to non-empty db

Revert I8bdd8c01349b3cb2a4b1ab79a048c09479c23f27 .

Refuse to restore to a non-empty database.

Bug-Url: https://bugzilla.redhat.com/1020277
Change-Id: I83d500e2a59e30d40c15cbde82b84d12206028dd
Signed-off-by: Yedidyah Bar David <didi@redhat.com>