Set cluster_name for PostgresNode.pm instances

This can help identifying test instances more easily at run time, and
it also provides some minimal test coverage for the cluster_name
feature.

Reviewed-by: Euler Taveira <euler@timbira.com.br>
Discussion: https://www.postgresql.org/message-id/flat/1257eaee-4874-e791-e83a-46720c72cac7@2ndquadrant.com

Author: petere

src/test/perl/PostgresNode.pm

@@ -700,8 +700,10 @@ sub start
 	my $name   = $self->name;
 	BAIL_OUT("node \"$name\" is already running") if defined $self->{_pid};
 	print("### Starting node \"$name\"\n");
+	# Note: We set the cluster_name here, not in postgresql.conf (in
+	# sub init) so that it does not get copied to standbys.
 	my $ret = TestLib::system_log('pg_ctl', '-D', $self->data_dir, '-l',
-		$self->logfile, 'start');
+		$self->logfile, '-o', "--cluster-name=$name", 'start');
 
 	if ($ret != 0)
 	{