Avoid creating filer folder if not starting it.

go/weed/server.go

@@ -140,10 +140,12 @@ func runServer(cmd *Command, args []string) bool {
 	if *masterMetaFolder == "" {
 		*masterMetaFolder = folders[0]
 	}
+	if *isStartingFiler {
 		if *filerOptions.dir == "" {
 			*filerOptions.dir = *masterMetaFolder + "/filer"
 			os.MkdirAll(*filerOptions.dir, 0700)
 		}
+	}
 	if err := util.TestFolderWritable(*masterMetaFolder); err != nil {
 		glog.Fatalf("Check Meta Folder (-mdir=\"%s\") Writable: %s", *masterMetaFolder, err)
 	}