Clean up nodes that are no longer of use in 007_pgdumpall.pl

Oversight in commit 763aaa06f0. When nodes are going out of scope, we
should stop the underlying postmasters rather than waiting for the
script to end.

Per gripe from Tom Lane

Discussion: https://postgr.es/m/740033.1772142754@sss.pgh.pa.us

src/bin/pg_dump/t/007_pg_dumpall.pl

@@ -352,6 +352,9 @@ foreach my $run (sort keys %pgdumpall_runs)
 			$pgdumpall_runs{$run}->{unlike},
 			"should not dump $run");
 	}
+
+	$target_node->stop;
+	$target_node->clean_node;
 }
 
 # Some negative test case with dump of pg_dumpall and restore using pg_restore