packaging: setup: turn engine.conf to ghost

this file should not be used as drop dir resolves the rpmnew/rpmsave
hell.

it must remain as ghost for backward compatibility.

Related-To: https://bugzilla.redhat.com/show_bug.cgi?id=1020675
Change-Id: I68ada5e69ec8fc255013b29ad47134f30bacd758
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>