[upgrade] don't create postgresql in "pre" script

If we attempt to create postgres user before running eDeploy upgrade,
that means the UID/GID will be different.

Tested in CI with pre script:
postgres:x:130:100::/home/postgres:/bin/bash

Without pre script:
postgres:x:180:180:PostgreSQL
administrator,,,:/var/lib/postgresql:/bin/bash
(what is managed by RH7.0-ids.tables file).