Make pg_upgrade's test.sh less chatty.

Make pg_upgrade's test.sh less chatty.

The use of "set -x" to echo a subset of the test's commands might've
been a good idea during development of this test, but it's been stable
for long enough now that the extra output isn't very useful.  Also
our project expectations have been trending towards less output in
non-error cases; the fact that "set -x" produces output on stderr
is particularly annoying from that standpoint.  So get rid of it.

Also, pass "-A trust" to initdb explicitly so that it won't issue
a warning about "trust" being an insecure default.  This matches
what the TAP tests have done for a long time, and again gets rid
of some noise on stderr.

Discussion: https://postgr.es/m/21766.1558397960@sss.pgh.pa.us