Support PostgresNode->new along with get_new_node in tests

PostgreSQL recently dropped nonstandard way of create PostgesNode object -
function get_new_node exported from the PostgresNode module.
Now it is recommended to use PostgresNode->new constructor call

This commit supports both ways of node creation - if get_new_node exists,
use it, otherwice all constructor directly.

Author: vbwagner

Diff for: t/001_basic.pl

@@ -18,7 +18,13 @@
 my $res_stderr;
 
 # Initialize node
-$node = get_new_node('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");
+}
 $node->init;
 $node->start;