packaging: engine-service: do not allow execution as non-root

all downstream has a mean to execute the script under the correct
account. So no need for us to change identity nor expect other user.

Change-Id: Ic30ce5316918a98bf2ef4cbf17d0eb91b85c74d1
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>