Authorize new user in pg_basebackup tests

Commit 8e2b6d45a0 added a new unprivileged user for testing
pg_basebackup, but omitted to add them to the cluster's authorized
logins, breaking Windows  tests run without using Unix sockets.

src/bin/pg_basebackup/t/010_pg_basebackup.pl

@@ -31,7 +31,8 @@ my @pg_basebackup_defs = ('pg_basebackup', '--no-sync', '-cfast');
 umask(0077);
 
 # Initialize node without replication settings
-$node->init(extra => ['--data-checksums']);
+$node->init(extra => ['--data-checksums'],
+			auth_extra => [ '--create-role', 'backupuser' ]);
 $node->start;
 my $pgdata = $node->data_dir;