Fix persistence references in tools subdir.

These had escaped me because the tools aren't rebuilt if there are
changes outside of the respective tool itself.

Change-Id: I3e69631babdd95b18e698eb79098dfa59f60f597

tools/dumper/main.go

@@ -76,7 +76,7 @@ func main() {
 		glog.Fatal("Must provide a path...")
 	}
 
-	persistence, err := tiered.NewLevelDBMetricPersistence(*storageRoot)
+	persistence, err := tiered.NewLevelDBPersistence(*storageRoot)
 	if err != nil {
 		glog.Fatal(err)
 	}

tools/pruner/main.go

@@ -35,7 +35,7 @@ func main() {
 		glog.Fatal("Must provide a path...")
 	}
 
-	persistences, err := tiered.NewLevelDBMetricPersistence(*storageRoot)
+	persistences, err := tiered.NewLevelDBPersistence(*storageRoot)
 	if err != nil {
 		glog.Fatal(err)
 	}