Make pg_upgrade's test.sh less chatty.

Make pg_upgrade's test.sh less chatty.

Remove "set -x", and pass "-A trust" to initdb explicitly,
to suppress almost all of the noise this script used to emit
on stderr.

This back-patches commit eb9812f27 into out-of-support branches,
pursuant to newly-established project policy.  The point is to
suppress useless noise on stderr when running check-world.

Discussion: https://postgr.es/m/d0316012-ece7-7b7e-2d36-9c38cb77cb3b@enterprisedb.com