PGPRO-5983: fix Perl tests due to changes in PostgreSQL 15devel

The standard PostgreSQL Perl modules for testing have been moved and some have
been renamed. Try to maintain both old and new modules by checking if we can
load new modules and loading the necessary modules at compile time. We cannot
load these modules at runtime because they can have INIT blocks.

Also use Perl's 'eval' function to call functions from these modules so we don't
get compilation errors due to conditionally loading modules.

Author: Marina Polyakova

t/001_basic.pl

@@ -6,25 +6,52 @@
 
 use strict;
 use warnings;
-use PostgresNode;
-use TestLib;
 use Test::More;
 
+my $pg_15_modules;
+
+BEGIN
+{
+	$pg_15_modules = eval
+	{
+		require PostgreSQL::Test::Cluster;
+		require PostgreSQL::Test::Utils;
+		return 1;
+	};
+
+	unless (defined $pg_15_modules)
+	{
+		$pg_15_modules = 0;
+
+		require PostgresNode;
+		require TestLib;
+	}
+}
+
 plan tests => 24;
 
+note('PostgreSQL 15 modules are used: ' . ($pg_15_modules ? 'yes' : 'no'));
+
 my $node;
 my $res;
 my $res_stdout;
 my $res_stderr;
 
-# Initialize node
-# Older version of PostgresNode.pm use get_new_node function.
-# Newer use standard perl object constructor syntax
-if (PostgresNode->can('get_new_node')) {
-	$node = get_new_node('node');
-} else {
-	$node = PostgresNode->new("node");
-}
+# Create node.
+# Older versions of PostgreSQL modules use get_new_node function.
+# Newer use standard perl object constructor syntax.
+eval
+{
+	if ($pg_15_modules)
+	{
+		$node = PostgreSQL::Test::Cluster->new("node");
+	}
+	else
+	{
+		$node = PostgresNode::get_new_node("node");
+	}
+};
+
 $node->init;
 $node->start;