playground: Set terminal title

This sets the terminal title to "TiUP Playground: <name>" where name
is the last part of the datadir. With `tiup -T foobar playground` etc.
this name can be set. Also `tiup client` uses the same names.

components/playground/main.go

@@ -595,6 +595,9 @@ func newEtcdClient(endpoint string) (*clientv3.Client, error) {
 }
 
 func main() {
+	dataDir := os.Getenv(localdata.EnvNameInstanceDataDir)
+	instanceName := dataDir[strings.LastIndex(dataDir, "/")+1:]
+	fmt.Printf("\033]0;TiUP Playground: %s\a", instanceName)
 	start := time.Now()
 	code := 0
 	err := execute()