Milo: Add themed page for errors

milo/appengine/buildbot/builder.go

 // Copyright 2016 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 buildbot
 
 import (
         "fmt"
         "net/http"
         "sort"
@@ skipping 60 matching lines @@
         if err != nil {
                 return nil, err
         }
         for _, b := range buildbots {
                 result = append(result, getBuildSummary(b))
         }
         return result, nil
 }
 
 var errMasterNotFound = miloerror.Error{
-        Message: "Master not found",
+        Message: "Either the request resource was not found or you are not authorized",
         Code:    http.StatusNotFound,
 }
 
+var errNotAuth = miloerror.Error{
+        Message: "You are not authenticated, try logging in",
+        Code:    http.StatusUnauthorized,
+}
+
 // builderImpl is the implementation for getting a milo builder page from buildbot.
 // This gets:
 // * Current Builds from querying the master json from the datastore.
 // * Recent Builds from a cron job that backfills the recent builds.
 func builderImpl(c context.Context, masterName, builderName string, limit int) (*resp.Builder, error) {
         result := &resp.Builder{
                 Name: builderName,
         }
         master, t, err := getMasterJSON(c, masterName)
         if err != nil {
@@ skipping 55 matching lines @@
         }
         result.CurrentBuilds = currentBuilds
 
         for _, fb := range finishedBuilds {
                 if fb != nil {
                         result.FinishedBuilds = append(result.FinishedBuilds, fb)
                 }
         }
         return result, nil
 }