packaging: setup: weird message on cleanup if no db

Make engine-cleanup continue gracefully if the database was manually
deleted.

Change-Id: Iaba0ba1563acbf8c0ef900b304aa577a3dd1f615
Bug-Url: https://bugzilla.redhat.com/1015037
Signed-off-by: Yedidyah Bar David <didi@redhat.com>