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.

Back-patch of commit eb9812f2 into all active branches.

Discussion: https://postgr.es/m/21766.1558397960@sss.pgh.pa.us
Discussion: https://postgr.es/m/20190722193459.GA14241@alvherre.pgsql