packaging: use $0 instead of hardcoding script name when calling
engine-upgrade

This patch solves confusing message being displayed by engine-upgrade if
it's being called by a softlink.
when the script displayed which filename is obsolete, it will display
the correct name

Change-Id: Idb1b517a1f5126161bffaf4d3efcfc0fabfa443a
Signed-off-by: Ohad Basan <obasan@redhat.com>