tsmon: read hostname and region from config file

common/tsmon/config.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package tsmon
 
 import (
         "encoding/json"
         "os"
         "runtime"
 )
 
 // config is the representation of a tsmon JSON config file.
 type config struct {
         Endpoint        string `json:"endpoint"`
         Credentials     string `json:"credentials"`
         AutoGenHostname bool   `json:"autogen_hostname"`
+        Hostname        string `json:"hostname"`
+        Region          string `json:"region"`
 }
 
 // loadConfig loads a tsmon JSON config from a file.
 func loadConfig(path string) (config, error) {
         var ret config
 
         file, err := os.Open(path)
         if err != nil {
                 return ret, err
         }
         defer file.Close()
 
         decoder := json.NewDecoder(file)
         if err = decoder.Decode(&ret); err != nil {
                 return ret, err
         }
 
         return ret, nil
 }
 
 func defaultConfigFilePath() string {
         if runtime.GOOS == "windows" {
                 return "C:\\chrome-infra\\ts-mon.json"
         }
         return "/etc/chrome-infra/ts-mon.json"
 }