Fix failures with TAP tests of pg_ctl on Windows

On Windows, all the hosts spawned by the TAP tests bind to 127.0.0.1.
Hence, if there is a port conflict, starting a cluster would immediately
fail.  One of the test scripts of pg_ctl initializes a node without
PostgresNode.pm, using the default port 5432.  This could cause
unexpected startup failures in the tests if an independent server was up
and running on the same host (the reverse is also possible, though more
unlikely).  Fix this issue by assigning properly a free port to the node
configured, in the same range used as for the other nodes part of the
tests.

Author: Michael Paquier
Reviewed-by: Andrew Dunstan
Discussion: https://postgr.es/m/20191202031444.GC1696@paquier.xyz
Backpatch-through: 11

src/bin/pg_ctl/t/001_start_stop.pl

@@ -22,8 +22,10 @@ command_ok([ 'pg_ctl', 'initdb', '-D', "$tempdir/data", '-o', '-N' ],
 	'pg_ctl initdb');
 command_ok([ $ENV{PG_REGRESS}, '--config-auth', "$tempdir/data" ],
 	'configure authentication');
+my $node_port = get_free_port();
 open my $conf, '>>', "$tempdir/data/postgresql.conf";
 print $conf "fsync = off\n";
+print $conf "port = $node_port\n";
 print $conf TestLib::slurp_file($ENV{TEMP_CONFIG})
   if defined $ENV{TEMP_CONFIG};