PostgresNode::backup uses spread checkpoint?

[Alvaro Herrera]

I noticed a few days ago that method backup() in PostgresNode uses
pg_basebackup without specifying a checkpoint mode -- and the default is
a spread checkpoint, which may cause any tests that use that to take
slightly longer than the bare minimum.

I propose to make it use a fast checkpoint, as per the attached.

-- 
Álvaro Herrera

diff --git a/src/test/perl/PostgresNode.pm b/src/test/perl/PostgresNode.pm
index 81ad42916b..72d8393fca 100644
--- a/src/test/perl/PostgresNode.pm
+++ b/src/test/perl/PostgresNode.pm
@@ -551,7 +551,7 @@ sub backup
 
 	print "# Taking pg_basebackup $backup_name from node \"$name\"\n";
 	TestLib::system_or_bail('pg_basebackup', '-D', $backup_path, '-h',
-		$self->host, '-p', $self->port, '--no-sync');
+		$self->host, '-p', $self->port, '-cfast', '--no-sync');
 	print "# Backup finished\n";
 	return;
 }