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

milo/appengine/job_source/buildbucket/properties.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 buildbucket
 
 import (
         "bytes"
         "strconv"
 )
@@ skipping 52 matching lines @@
         BuilderName string `json:"builder_name"`
         Properties  properties
         Changes     []change
 }
 
 // resultDetails is contents of "result_details_json" buildbucket build field
 // in the format supported by Buildbot.
 type resultDetails struct {
         Properties properties
 }