[milo] {buildbucket,buildbot,swarming,logdog} -> backends/*.

milo/appengine/backends/buildbucket/buckets.go

 // Copyright 2017 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 buildbucket
 
 import (
         "errors"
         "fmt"
 
@@ skipping 29 matching lines @@
                 group.Builders = make([]resp.Link, len(bucket.Builders))
                 for j, builder := range bucket.Builders {
                         group.Builders[j] = *resp.NewLink(
                                 builder.Name, fmt.Sprintf("/buildbucket/%s/%s", bucket.Name, builder.Name))
                 }
                 result.BuilderGroups[i] = group
         }
 
         return result, nil
 }